diff --git a/internal/docsite/checks_test.go b/internal/docsite/checks_test.go
index 221173a..70efd4b 100644
--- a/internal/docsite/checks_test.go
+++ b/internal/docsite/checks_test.go
@@ -469,6 +469,140 @@ func TestCommandTokenForms(t *testing.T) {
 	})
 }
 
+func TestNestedFenceChecks(t *testing.T) {
+	body := strings.Join([]string{
+		"> [!NOTE]",
+		"> ```go",
+		"> x := 1",
+		"> ```",
+		"",
+		"- item",
+		"",
+		"  ```go",
+		"  x := 1",
+		"  ```",
+		"",
+		"```GO",
+		"x := 1",
+		"```",
+		"",
+		"```main.go",
+		"x := 1",
+		"```",
+		"",
+		"    ```go",
+		"    x := 1",
+		"    ```",
+		"",
+		"> [!NOTE]",
+		"> ```sh",
+		"> summer bogus:nested",
+		"> ```",
+		"",
+		"> ```yaml src=config/app.yaml",
+		"> app:",
+		"> ```",
+		"",
+	}, "\n")
+	readme := strings.Join([]string{
+		"# fixture",
+		"",
+		"Fixture does one thing.",
+		"",
+		"## Usage",
+		"",
+		"```go",
+		"x := 1",
+		"```",
+		"",
+		"```go src=modules/fixture/fixture.go",
+		"package fixture",
+		"```",
+		"",
+	}, "\n")
+	assertProblems(t, checkFixture(t, fixtureCommands, map[string]string{
+		"docs/index.md":             page("Acme docs", "index", 0, "Text.\n"),
+		"docs/setup/start.md":       page("Start", "setup", 10, body),
+		"modules/fixture/README.md": readme,
+	}), []string{
+		"docs/setup/start.md:10: snippet: go code block has no src= reference",
+		"docs/setup/start.md:16: snippet: go code block has no src= reference",
+		"docs/setup/start.md:20: snippet: GO code block has no src= reference",
+		"docs/setup/start.md:24: snippet: main.go code block has no src= reference",
+		`docs/setup/start.md:34: command: "bogus:nested" is not a summer or application command`,
+		"docs/setup/start.md:37: snippet: config/app.yaml: " + nestedSrcMessage,
+		"modules/fixture/README.md:11: snippet: modules/fixture/fixture.go: " + readmeSrcMessage,
+	})
+}
+
+func TestIdentifierGoDocCaseSensitive(t *testing.T) {
+	root := writeTree(t, map[string]string{
+		"go.mod": "module example.com/forms\n\ngo 1.27\n",
+		"modules/forms/forms.go": "package forms\n\n" +
+			"// OpenFromApp is a fixture.\nfunc OpenFromApp() {}\n\n" +
+			"// Outer holds a method.\ntype Outer struct{}\n\n" +
+			"// HelloWorld is a method.\nfunc (Outer) HelloWorld() {}\n",
+	})
+	idx, problems, err := buildIdentIndex(root)
+	if err != nil || len(problems) > 0 {
+		t.Fatalf("buildIdentIndex: %v %q", err, problemLines(problems))
+	}
+	for _, q := range []string{"OpenFromApp", "Outer.HelloWorld"} {
+		if !idx.goDoc("modules/forms", q) {
+			t.Errorf("goDoc(%q) = false, want true", q)
+		}
+	}
+	for _, q := range []string{"Openfromapp", "Outer.Helloworld"} {
+		if idx.goDoc("modules/forms", q) {
+			t.Errorf("goDoc(%q) = true, want false", q)
+		}
+	}
+	if got := idx.checkSpan("forms.Openfromapp"); got != "forms.Openfromapp does not exist in modules/forms" {
+		t.Fatalf("checkSpan = %q", got)
+	}
+}
+
+func TestCommandWord(t *testing.T) {
+	tool, app := true, false
+	cases := []struct {
+		in       string
+		name     string
+		tool, ok bool
+	}{
+		{"summer docs:build", "docs:build", tool, true},
+		{"$ summer docs:build --out site", "docs:build", tool, true},
+		{"FOO=1 summer no:such", "no:such", tool, true},
+		{"FOO=1 BAR=x ./bin/acme serve", "serve", app, true},
+		{"summer --root . no:such", "no:such", tool, true},
+		{"summer --root=. docs:build", "docs:build", tool, true},
+		{"summer -r . docs:build", "docs:build", tool, true},
+		{"summer --help", "", tool, false},
+		{"summer --help docs:build", "docs:build", tool, true},
+		{"summer -h docs:build", "docs:build", tool, true},
+		{"summer --root", "", tool, false},
+		{"summer --root .", "", tool, false},
+		{"summer -- docs:build", "", tool, false},
+		{"go run ./cmd/summer no:such", "no:such", tool, true},
+		{"go run ./cmd/summer --root . docs:build", "docs:build", tool, true},
+		{"bin/acme migrate", "migrate", app, true},
+		{"./bin/acme migrate", "migrate", app, true},
+		{"echo summer x", "", false, false},
+		{"# summer x", "", false, false},
+		{"go test ./modules/demo", "", false, false},
+		{"go install ./cmd/summer", "", false, false},
+		{"summer", "", tool, false},
+		{"FOO=1", "", false, false},
+		{"summer --version", "", tool, false},
+	}
+	for _, tc := range cases {
+		name, isTool, ok := commandWord(tc.in)
+		if name != tc.name || isTool != tc.tool || ok != tc.ok {
+			t.Errorf("commandWord(%q) = %q, %v, %v; want %q, %v, %v",
+				tc.in, name, isTool, ok, tc.name, tc.tool, tc.ok)
+		}
+	}
+}
+
 func TestExampleCommandNames(t *testing.T) {
 	dir := writeTree(t, map[string]string{
 		"a/main.go": "package main\n\nimport \"x/bonfire\"\n\nvar a = bonfire.Command{Name: \"a:one\", Description: \"d\"}\n" +
diff --git a/internal/docsite/fences_test.go b/internal/docsite/fences_test.go
new file mode 100644
index 0000000..6f9ebf5
--- /dev/null
+++ b/internal/docsite/fences_test.go
@@ -0,0 +1,84 @@
+package docsite
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestCollectFences(t *testing.T) {
+	body := strings.Join([]string{
+		"```go",
+		"top",
+		"```",
+		"",
+		"> [!TIP]",
+		"> ```go",
+		"> callout line",
+		"> ```",
+		"",
+		"> ```yaml",
+		"> quote line",
+		"> ```",
+		"",
+		"- item",
+		"",
+		"  ```go",
+		"  list line",
+		"  ```",
+		"",
+		"```",
+		"noinfo",
+		"```",
+		"",
+		"    ```",
+		"    four spaces",
+		"    ```",
+		"",
+		"```sh",
+		"unterminated",
+	}, "\n")
+	doc := (&site{}).parseRaw(newMarkdown(), []byte(body))
+	fences, err := collectFences(doc, []byte(body))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(fences) != 6 {
+		t.Fatalf("fences = %d, want 6 (four-space backticks are not a fence)", len(fences))
+	}
+	want := []struct {
+		info, code string
+		line       int
+		top        bool
+		close      int // -2 means top was not filled
+	}{
+		{"go", "top", 0, true, 2},
+		{"go", "callout line", 5, false, -2},
+		{"yaml", "quote line", 9, false, -2},
+		{"go", "list line", 15, false, -2},
+		{"", "noinfo", 19, true, -2},
+		{"sh", "unterminated", 27, true, -1},
+	}
+	for i, w := range want {
+		f := fences[i]
+		if f.info != w.info || f.line != w.line || f.topLevel != w.top {
+			t.Errorf("fence %d = info %q line %d top %v, want info %q line %d top %v",
+				i, f.info, f.line, f.topLevel, w.info, w.line, w.top)
+		}
+		if len(f.code) != 1 || f.code[0].text != w.code {
+			got := ""
+			if len(f.code) > 0 {
+				got = f.code[0].text
+			}
+			t.Errorf("fence %d code = %q, want %q", i, got, w.code)
+		}
+		if w.close != -2 && f.top.close != w.close {
+			t.Errorf("fence %d top.close = %d, want %d", i, f.top.close, w.close)
+		}
+	}
+	if _, ok := openFence("   ```go"); !ok {
+		t.Error("openFence rejected three leading spaces")
+	}
+	if _, ok := openFence("    ```go"); ok {
+		t.Error("openFence accepted four leading spaces")
+	}
+}
diff --git a/internal/docsite/highlight_test.go b/internal/docsite/highlight_test.go
index 65cc6b4..bf0873d 100644
--- a/internal/docsite/highlight_test.go
+++ b/internal/docsite/highlight_test.go
@@ -150,3 +150,16 @@ func TestHighlightFenceMarkup(t *testing.T) {
 		t.Error("a fence without src= has a caption")
 	}
 }
+
+func TestGoLang(t *testing.T) {
+	for _, lang := range []string{"go", "Go", "GO", "golang", "Golang", "main.go"} {
+		if !goLang(lang) {
+			t.Errorf("goLang(%q) = false, want true", lang)
+		}
+	}
+	for _, lang := range []string{"go-html-template", "go-text-template", "text", "yaml", "sh", ""} {
+		if goLang(lang) {
+			t.Errorf("goLang(%q) = true, want false", lang)
+		}
+	}
+}
diff --git a/internal/docsite/render_test.go b/internal/docsite/render_test.go
index 15a8082..10aa648 100644
--- a/internal/docsite/render_test.go
+++ b/internal/docsite/render_test.go
@@ -71,6 +71,36 @@ func renderHTML(t *testing.T, s *site, p *Page) renderedPage {
 	return r
 }
 
+func TestFenceCaptionsOnlyVerified(t *testing.T) {
+	guide := page("Start", "setup", 10, strings.Join([]string{
+		"```go src=pkg/lib.go#Greeting",
+		"func Greeting() {}",
+		"```",
+		"",
+		"> [!TIP]",
+		"> ```go src=pkg/lib.go#Greeting",
+		"> func stale() {}",
+		"> ```",
+		"",
+	}, "\n"))
+	readme := "# alpha\n\nAlpha does one thing.\n\n```go src=modules/alpha/alpha.go\npackage alpha\n```\n"
+	s, pages := renderFixture(t, map[string]string{
+		"docs/setup/start.md":     guide,
+		"modules/alpha/README.md": readme,
+	})
+	guideHTML := string(renderHTML(t, s, pages["setup/start"]).html)
+	if got := strings.Count(guideHTML, "<figcaption>"); got != 1 {
+		t.Fatalf("guide figcaptions = %d, want 1\n%s", got, guideHTML)
+	}
+	if !strings.Contains(guideHTML, "<figcaption>pkg/lib.go#Greeting</figcaption>") {
+		t.Fatalf("guide caption missing the top-level reference\n%s", guideHTML)
+	}
+	readmeHTML := string(renderHTML(t, s, pages["api/alpha"]).html)
+	if strings.Contains(readmeHTML, "<figcaption>") {
+		t.Fatalf("module README has a caption\n%s", readmeHTML)
+	}
+}
+
 func TestLinkRewriting(t *testing.T) {
 	body := strings.Join([]string{
 		"- [start](setup/start.md)",
diff --git a/internal/docsite/snippet_test.go b/internal/docsite/snippet_test.go
index b3a6fc0..471ef14 100644
--- a/internal/docsite/snippet_test.go
+++ b/internal/docsite/snippet_test.go
@@ -3,6 +3,7 @@ package docsite
 import (
 	"os"
 	"path/filepath"
+	"runtime"
 	"slices"
 	"strings"
 	"testing"
@@ -320,3 +321,160 @@ func TestSnippetTestGraph(t *testing.T) {
 		t.Errorf("Extract with an unparsable sibling test = %v", err)
 	}
 }
+
+func TestSnippetRootsAndBuild(t *testing.T) {
+	other := "windows"
+	if runtime.GOOS == "windows" {
+		other = "linux"
+	}
+	root := writeTree(t, map[string]string{
+		"p/p.go": "package p\n",
+		"p/p_test.go": `package p
+
+import "testing"
+
+func Test(t *testing.T) { fromTest() }
+func Test_x(t *testing.T) { fromTestX() }
+func TestMain(m *testing.M) { fromMain() }
+func Testable() { fromTestable() }
+
+func fromTest() {}
+func fromTestX() {}
+func fromMain() {}
+func fromTestable() {}
+func onlyFromIgnored() {}
+
+func ExampleOut() {
+	fromOut()
+	// Output: out
+}
+
+func ExampleEmpty() {
+	fromEmpty()
+	// Output:
+}
+
+func ExampleNone() {
+	fromNone()
+}
+
+func fromOut() {}
+func fromEmpty() {}
+func fromNone() {}
+`,
+		"p/ignored_test.go":       "//go:build ignore\n\npackage p\n\nimport \"testing\"\n\nfunc TestIgnored(t *testing.T) { onlyFromIgnored() }\n",
+		"p/broken.go":             "//go:build ignore\n\npackage p\n\nfunc Broken() {}\n",
+		"p/broken_test.go":        "//go:build ignore\n\npackage p\n\nfunc IgnoredTestTarget() {}\n",
+		"p/only_" + other + ".go": "package p\n\nfunc OnlyOS() {}\n",
+		"p/testdata/skip.go":      "package p\n\nfunc Skip() {}\n",
+		"p/_old/old.go":           "package p\n\nfunc Old() {}\n",
+		"p/testdata/app.yaml":     "# docs:start db\nhost: localhost\n# docs:end db\n",
+	})
+	g, err := loadTestGraph(filepath.Join(root, "p"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, name := range []string{"Test", "Test_x", "TestMain", "ExampleOut", "ExampleEmpty", "fromTest", "fromTestX", "fromMain", "fromOut", "fromEmpty"} {
+		if !g.reachable[name] {
+			t.Errorf("%s is not a root or reachable from one", name)
+		}
+	}
+	for _, name := range []string{"Testable", "ExampleNone", "fromTestable", "fromNone", "onlyFromIgnored", "TestIgnored"} {
+		if g.reachable[name] {
+			t.Errorf("%s is reachable, want it not run", name)
+		}
+	}
+	mustExtract := func(ref Ref, wantErr string) {
+		t.Helper()
+		_, err := Extract(root, ref)
+		if wantErr == "" {
+			if err != nil {
+				t.Errorf("Extract(%s) = %v, want nil", ref, err)
+			}
+			return
+		}
+		if err == nil || !strings.Contains(err.Error(), wantErr) {
+			t.Errorf("Extract(%s) = %v, want %q", ref, err, wantErr)
+		}
+	}
+	skipped := "file is in a directory go test ./... skips"
+	excluded := "file is excluded from the default build"
+	mustExtract(Ref{"p/p_test.go", "fromOut"}, "")
+	mustExtract(Ref{"p/p_test.go", "fromEmpty"}, "")
+	mustExtract(Ref{"p/p_test.go", "fromNone"}, notRunMessage)
+	mustExtract(Ref{"p/p_test.go", "fromTestable"}, notRunMessage)
+	mustExtract(Ref{"p/p_test.go", "onlyFromIgnored"}, notRunMessage)
+	mustExtract(Ref{"p/broken.go", "Broken"}, excluded)
+	mustExtract(Ref{"p/broken_test.go", "IgnoredTestTarget"}, excluded)
+	mustExtract(Ref{"p/only_" + other + ".go", "OnlyOS"}, excluded)
+	mustExtract(Ref{"p/testdata/skip.go", "Skip"}, skipped)
+	mustExtract(Ref{"p/_old/old.go", "Old"}, skipped)
+	got, err := Extract(root, Ref{"p/testdata/app.yaml", "db"})
+	if err != nil || got != "host: localhost" {
+		t.Fatalf("Extract yaml = %q, %v", got, err)
+	}
+}
+
+func TestSyncParsedFences(t *testing.T) {
+	callout := "> [!NOTE]\n> Keep this callout text.\n"
+	doc := page("Start", "setup", 10, "Intro.\n\n```go src=pkg/lib.go#Greeting\nfunc stale() {}\n```\n\n"+callout+"\nOutro.\n")
+	root := snippetTree(t, map[string]string{"docs/setup/start.md": doc})
+	path := filepath.Join(root, "docs/setup/start.md")
+	res, problems, err := Sync(Options{Root: root})
+	if err != nil || len(problems) > 0 {
+		t.Fatalf("Sync: %v %v", err, problems)
+	}
+	if res.Files != 1 || res.Snippets != 1 {
+		t.Fatalf("Sync = %+v, want 1 snippet in 1 file", res)
+	}
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantDoc := strings.Replace(doc, "func stale() {}\n",
+		"// Greeting returns a greeting.\nfunc Greeting(name string) string {\n\treturn \"Hello, \" + name\n}\n", 1)
+	if string(got) != wantDoc {
+		t.Fatalf("synced file =\n%s\nwant\n%s", got, wantDoc)
+	}
+	if !strings.HasPrefix(string(got), "---\ntitle: Start\n") || !strings.Contains(string(got), callout) {
+		t.Fatal("frontmatter or callout text changed")
+	}
+
+	nested := page("Start", "setup", 10, "Intro.\n\n> [!NOTE]\n> ```go src=pkg/lib.go#Greeting\n> func stale() {}\n> ```\n\nOutro.\n")
+	root = snippetTree(t, map[string]string{"docs/setup/start.md": nested})
+	before := map[string]string{}
+	err = filepath.WalkDir(root, func(p string, d os.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return err
+		}
+		b, err := os.ReadFile(p)
+		if err != nil {
+			return err
+		}
+		before[p] = string(b)
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	res, problems, err = Sync(Options{Root: root})
+	if err != nil || res != (SyncResult{}) || len(problems) != 1 || !strings.Contains(problems[0].Message, nestedSrcMessage) {
+		t.Fatalf("nested Sync = %+v %q %v", res, problemLines(problems), err)
+	}
+	err = filepath.WalkDir(root, func(p string, d os.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return err
+		}
+		b, err := os.ReadFile(p)
+		if err != nil {
+			return err
+		}
+		if string(b) != before[p] {
+			t.Errorf("Sync changed %s", p)
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+}
diff --git a/internal/docsite/testdata/violations/command-bin-no-dot/docs/extras/faq.md b/internal/docsite/testdata/violations/command-bin-no-dot/docs/extras/faq.md
new file mode 100644
index 0000000..270b867
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-bin-no-dot/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```sh
+bin/demo no:such
+```
diff --git a/internal/docsite/testdata/violations/command-bin-no-dot/want.txt b/internal/docsite/testdata/violations/command-bin-no-dot/want.txt
new file mode 100644
index 0000000..d5f59c5
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-bin-no-dot/want.txt
@@ -0,0 +1,3 @@
+rule: command
+file: docs/extras/faq.md
+message: "no:such" is not a summer or application command
diff --git a/internal/docsite/testdata/violations/command-env-prefix/docs/extras/faq.md b/internal/docsite/testdata/violations/command-env-prefix/docs/extras/faq.md
new file mode 100644
index 0000000..539fb50
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-env-prefix/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```sh
+FOO=1 summer no:such
+```
diff --git a/internal/docsite/testdata/violations/command-env-prefix/want.txt b/internal/docsite/testdata/violations/command-env-prefix/want.txt
new file mode 100644
index 0000000..d5f59c5
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-env-prefix/want.txt
@@ -0,0 +1,3 @@
+rule: command
+file: docs/extras/faq.md
+message: "no:such" is not a summer or application command
diff --git a/internal/docsite/testdata/violations/command-flag-first/docs/extras/faq.md b/internal/docsite/testdata/violations/command-flag-first/docs/extras/faq.md
new file mode 100644
index 0000000..629ae47
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-flag-first/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```sh
+summer --root . no:such
+```
diff --git a/internal/docsite/testdata/violations/command-flag-first/want.txt b/internal/docsite/testdata/violations/command-flag-first/want.txt
new file mode 100644
index 0000000..d5f59c5
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-flag-first/want.txt
@@ -0,0 +1,3 @@
+rule: command
+file: docs/extras/faq.md
+message: "no:such" is not a summer or application command
diff --git a/internal/docsite/testdata/violations/command-go-run/docs/extras/faq.md b/internal/docsite/testdata/violations/command-go-run/docs/extras/faq.md
new file mode 100644
index 0000000..c2d6cab
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-go-run/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```sh
+go run ./cmd/summer no:such
+```
diff --git a/internal/docsite/testdata/violations/command-go-run/want.txt b/internal/docsite/testdata/violations/command-go-run/want.txt
new file mode 100644
index 0000000..d5f59c5
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-go-run/want.txt
@@ -0,0 +1,3 @@
+rule: command
+file: docs/extras/faq.md
+message: "no:such" is not a summer or application command
diff --git a/internal/docsite/testdata/violations/command-in-callout/docs/extras/faq.md b/internal/docsite/testdata/violations/command-in-callout/docs/extras/faq.md
new file mode 100644
index 0000000..17141ed
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-in-callout/docs/extras/faq.md
@@ -0,0 +1,20 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+> [!NOTE]
+> ```sh
+> summer no:such
+> ```
diff --git a/internal/docsite/testdata/violations/command-in-callout/want.txt b/internal/docsite/testdata/violations/command-in-callout/want.txt
new file mode 100644
index 0000000..d5f59c5
--- /dev/null
+++ b/internal/docsite/testdata/violations/command-in-callout/want.txt
@@ -0,0 +1,3 @@
+rule: command
+file: docs/extras/faq.md
+message: "no:such" is not a summer or application command
diff --git a/internal/docsite/testdata/violations/go-fence-callout-no-src/docs/extras/faq.md b/internal/docsite/testdata/violations/go-fence-callout-no-src/docs/extras/faq.md
new file mode 100644
index 0000000..e03f128
--- /dev/null
+++ b/internal/docsite/testdata/violations/go-fence-callout-no-src/docs/extras/faq.md
@@ -0,0 +1,20 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+> [!NOTE]
+> ```go
+> x := 1
+> ```
diff --git a/internal/docsite/testdata/violations/go-fence-callout-no-src/want.txt b/internal/docsite/testdata/violations/go-fence-callout-no-src/want.txt
new file mode 100644
index 0000000..83d9670
--- /dev/null
+++ b/internal/docsite/testdata/violations/go-fence-callout-no-src/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: go code block has no src= reference
diff --git a/internal/docsite/testdata/violations/go-fence-golang/docs/extras/faq.md b/internal/docsite/testdata/violations/go-fence-golang/docs/extras/faq.md
new file mode 100644
index 0000000..2839343
--- /dev/null
+++ b/internal/docsite/testdata/violations/go-fence-golang/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```golang
+x := 1
+```
diff --git a/internal/docsite/testdata/violations/go-fence-golang/want.txt b/internal/docsite/testdata/violations/go-fence-golang/want.txt
new file mode 100644
index 0000000..758b11b
--- /dev/null
+++ b/internal/docsite/testdata/violations/go-fence-golang/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: golang code block has no src= reference
diff --git a/internal/docsite/testdata/violations/identifier-wrong-case/docs/extras/faq.md b/internal/docsite/testdata/violations/identifier-wrong-case/docs/extras/faq.md
new file mode 100644
index 0000000..797f427
--- /dev/null
+++ b/internal/docsite/testdata/violations/identifier-wrong-case/docs/extras/faq.md
@@ -0,0 +1,17 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+Call `demo.Openfromapp`.
diff --git a/internal/docsite/testdata/violations/identifier-wrong-case/modules/demo/open.go b/internal/docsite/testdata/violations/identifier-wrong-case/modules/demo/open.go
new file mode 100644
index 0000000..d56021d
--- /dev/null
+++ b/internal/docsite/testdata/violations/identifier-wrong-case/modules/demo/open.go
@@ -0,0 +1,4 @@
+package demo
+
+// OpenFromApp is a fixture.
+func OpenFromApp() {}
diff --git a/internal/docsite/testdata/violations/identifier-wrong-case/want.txt b/internal/docsite/testdata/violations/identifier-wrong-case/want.txt
new file mode 100644
index 0000000..82db385
--- /dev/null
+++ b/internal/docsite/testdata/violations/identifier-wrong-case/want.txt
@@ -0,0 +1,3 @@
+rule: identifier
+file: docs/extras/faq.md
+message: demo.Openfromapp does not exist in modules/demo
diff --git a/internal/docsite/testdata/violations/snippet-blockquote/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-blockquote/docs/extras/faq.md
new file mode 100644
index 0000000..10a3a1b
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-blockquote/docs/extras/faq.md
@@ -0,0 +1,24 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+> ```yaml src=config/app.yaml
+> app:
+>   # docs:start db
+>   db:
+>     host: localhost
+>     port: 5432
+>   # docs:end db
+> ```
diff --git a/internal/docsite/testdata/violations/snippet-blockquote/want.txt b/internal/docsite/testdata/violations/snippet-blockquote/want.txt
new file mode 100644
index 0000000..8e591e0
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-blockquote/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: config/app.yaml: src= code block must be a top-level block
diff --git a/internal/docsite/testdata/violations/snippet-build-ignored-test-root/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-build-ignored-test-root/docs/extras/faq.md
new file mode 100644
index 0000000..c7e2a0c
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-build-ignored-test-root/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```go src=modules/demo/demo_test.go#ignoredOnly
+func ignoredOnly() string { return "x" }
+```
diff --git a/internal/docsite/testdata/violations/snippet-build-ignored-test-root/modules/demo/demo_test.go b/internal/docsite/testdata/violations/snippet-build-ignored-test-root/modules/demo/demo_test.go
new file mode 100644
index 0000000..89d405d
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-build-ignored-test-root/modules/demo/demo_test.go
@@ -0,0 +1,15 @@
+package demo
+
+import "testing"
+
+func TestGreet(t *testing.T) {
+	// docs:start greet
+	g := Greeter{Name: "blog"}
+	got := g.Greet()
+	// docs:end greet
+	if got != "Hello, blog" {
+		t.Fatalf("Greet() = %q", got)
+	}
+}
+
+func ignoredOnly() string { return "x" }
diff --git a/internal/docsite/testdata/violations/snippet-build-ignored-test-root/modules/demo/ignored_test.go b/internal/docsite/testdata/violations/snippet-build-ignored-test-root/modules/demo/ignored_test.go
new file mode 100644
index 0000000..b5492ef
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-build-ignored-test-root/modules/demo/ignored_test.go
@@ -0,0 +1,7 @@
+//go:build ignore
+
+package demo
+
+import "testing"
+
+func TestIgnored(t *testing.T) { _ = ignoredOnly() }
diff --git a/internal/docsite/testdata/violations/snippet-build-ignored-test-root/want.txt b/internal/docsite/testdata/violations/snippet-build-ignored-test-root/want.txt
new file mode 100644
index 0000000..d8f2eaa
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-build-ignored-test-root/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: fragment is not inside a Test or Example function
diff --git a/internal/docsite/testdata/violations/snippet-build-ignored/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-build-ignored/docs/extras/faq.md
new file mode 100644
index 0000000..2f5a93c
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-build-ignored/docs/extras/faq.md
@@ -0,0 +1,20 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```go src=modules/demo/broken.go#Broken
+// Broken is never built.
+func Broken() { undefinedCall() }
+```
diff --git a/internal/docsite/testdata/violations/snippet-build-ignored/modules/demo/broken.go b/internal/docsite/testdata/violations/snippet-build-ignored/modules/demo/broken.go
new file mode 100644
index 0000000..d025da9
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-build-ignored/modules/demo/broken.go
@@ -0,0 +1,6 @@
+//go:build ignore
+
+package demo
+
+// Broken is never built.
+func Broken() { undefinedCall() }
diff --git a/internal/docsite/testdata/violations/snippet-build-ignored/want.txt b/internal/docsite/testdata/violations/snippet-build-ignored/want.txt
new file mode 100644
index 0000000..a025457
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-build-ignored/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: modules/demo/broken.go#Broken: file is excluded from the default build
diff --git a/internal/docsite/testdata/violations/snippet-callout-drift/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-callout-drift/docs/extras/faq.md
new file mode 100644
index 0000000..cbafc2b
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-callout-drift/docs/extras/faq.md
@@ -0,0 +1,20 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+> [!TIP]
+> ```go src=modules/demo/example_test.go#ExampleHello
+> BOGUS
+> ```
diff --git a/internal/docsite/testdata/violations/snippet-callout-drift/want.txt b/internal/docsite/testdata/violations/snippet-callout-drift/want.txt
new file mode 100644
index 0000000..c633912
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-callout-drift/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: modules/demo/example_test.go#ExampleHello: src= code block must be a top-level block
diff --git a/internal/docsite/testdata/violations/snippet-callout-missing/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-callout-missing/docs/extras/faq.md
new file mode 100644
index 0000000..7ce9876
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-callout-missing/docs/extras/faq.md
@@ -0,0 +1,20 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+> [!NOTE]
+> ```go src=modules/demo/missing_test.go#ExampleNope
+> fmt.Println()
+> ```
diff --git a/internal/docsite/testdata/violations/snippet-callout-missing/want.txt b/internal/docsite/testdata/violations/snippet-callout-missing/want.txt
new file mode 100644
index 0000000..c1fbd7a
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-callout-missing/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: modules/demo/missing_test.go#ExampleNope: src= code block must be a top-level block
diff --git a/internal/docsite/testdata/violations/snippet-example-no-output-helper/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-example-no-output-helper/docs/extras/faq.md
new file mode 100644
index 0000000..e51508e
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-example-no-output-helper/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```go src=modules/demo/never_test.go#neverRunHelper
+func neverRunHelper() {}
+```
diff --git a/internal/docsite/testdata/violations/snippet-example-no-output-helper/modules/demo/never_test.go b/internal/docsite/testdata/violations/snippet-example-no-output-helper/modules/demo/never_test.go
new file mode 100644
index 0000000..bc70206
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-example-no-output-helper/modules/demo/never_test.go
@@ -0,0 +1,7 @@
+package demo_test
+
+func Example_neverRun() {
+	neverRunHelper()
+}
+
+func neverRunHelper() {}
diff --git a/internal/docsite/testdata/violations/snippet-example-no-output-helper/want.txt b/internal/docsite/testdata/violations/snippet-example-no-output-helper/want.txt
new file mode 100644
index 0000000..d8f2eaa
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-example-no-output-helper/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: fragment is not inside a Test or Example function
diff --git a/internal/docsite/testdata/violations/snippet-example-no-output-region/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-example-no-output-region/docs/extras/faq.md
new file mode 100644
index 0000000..1312cd5
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-example-no-output-region/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```go src=modules/demo/never_test.go#never
+_ = 1
+```
diff --git a/internal/docsite/testdata/violations/snippet-example-no-output-region/modules/demo/never_test.go b/internal/docsite/testdata/violations/snippet-example-no-output-region/modules/demo/never_test.go
new file mode 100644
index 0000000..8aed2d2
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-example-no-output-region/modules/demo/never_test.go
@@ -0,0 +1,11 @@
+package demo_test
+
+func Example_neverRun() {
+	neverRunHelper()
+}
+
+func neverRunHelper() {
+	// docs:start never
+	_ = 1
+	// docs:end never
+}
diff --git a/internal/docsite/testdata/violations/snippet-example-no-output-region/want.txt b/internal/docsite/testdata/violations/snippet-example-no-output-region/want.txt
new file mode 100644
index 0000000..d8f2eaa
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-example-no-output-region/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: fragment is not inside a Test or Example function
diff --git a/internal/docsite/testdata/violations/snippet-list-item/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-list-item/docs/extras/faq.md
new file mode 100644
index 0000000..0f440e1
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-list-item/docs/extras/faq.md
@@ -0,0 +1,22 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+- Greet:
+
+  ```go src=modules/demo/example_test.go#ExampleHello
+  fmt.Println(demo.Hello("blog"))
+  // Output: Hello, blog
+  ```
diff --git a/internal/docsite/testdata/violations/snippet-list-item/want.txt b/internal/docsite/testdata/violations/snippet-list-item/want.txt
new file mode 100644
index 0000000..c633912
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-list-item/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: modules/demo/example_test.go#ExampleHello: src= code block must be a top-level block
diff --git a/internal/docsite/testdata/violations/snippet-readme-src/modules/demo/README.md b/internal/docsite/testdata/violations/snippet-readme-src/modules/demo/README.md
new file mode 100644
index 0000000..9f374b4
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-readme-src/modules/demo/README.md
@@ -0,0 +1,24 @@
+# demo
+
+Demo greets people by name.
+
+```go
+import "example.com/docfixture/modules/demo"
+```
+
+## Usage
+
+Call `demo.Hello` or build a `demo.Greeter` and call `demo.Greeter.Greet`.
+
+See the [start guide](../../docs/guide/start.md#install).
+
+## Testing
+
+```sh
+go test ./modules/demo
+```
+
+```go src=modules/demo/example_test.go#ExampleHello
+fmt.Println(demo.Hello("blog"))
+// Output: Hello, blog
+```
diff --git a/internal/docsite/testdata/violations/snippet-readme-src/want.txt b/internal/docsite/testdata/violations/snippet-readme-src/want.txt
new file mode 100644
index 0000000..715f409
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-readme-src/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: modules/demo/README.md
+message: modules/demo/example_test.go#ExampleHello: module README code blocks are rendered as written
diff --git a/internal/docsite/testdata/violations/snippet-testdata-go/docs/extras/faq.md b/internal/docsite/testdata/violations/snippet-testdata-go/docs/extras/faq.md
new file mode 100644
index 0000000..c218872
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-testdata-go/docs/extras/faq.md
@@ -0,0 +1,19 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```
+
+```go src=modules/demo/testdata/fixture_test.go#td
+_ = 1
+```
diff --git a/internal/docsite/testdata/violations/snippet-testdata-go/modules/demo/testdata/fixture_test.go b/internal/docsite/testdata/violations/snippet-testdata-go/modules/demo/testdata/fixture_test.go
new file mode 100644
index 0000000..6e811d1
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-testdata-go/modules/demo/testdata/fixture_test.go
@@ -0,0 +1,9 @@
+package demo
+
+import "testing"
+
+func TestFixture(t *testing.T) {
+	// docs:start td
+	_ = 1
+	// docs:end td
+}
diff --git a/internal/docsite/testdata/violations/snippet-testdata-go/want.txt b/internal/docsite/testdata/violations/snippet-testdata-go/want.txt
new file mode 100644
index 0000000..55d84d3
--- /dev/null
+++ b/internal/docsite/testdata/violations/snippet-testdata-go/want.txt
@@ -0,0 +1,3 @@
+rule: snippet
+file: docs/extras/faq.md
+message: file is in a directory go test ./... skips