Update section behavior

assets/editor/main.html

@@ -9,6 +9,7 @@
 </script>
 <form id="edit-form" class="edit-form" method="POST" action="{{.PostURL}}">
     {{if ge .SectionIndex 0}}<input type="hidden" name="section" value="{{.SectionIndex}}">{{end}}
+    {{if .Span}}<input type="hidden" name="span" value="1">{{end}}
     {{if ge .InsertBefore 0}}<input type="hidden" name="insert_before" value="{{.InsertBefore}}">{{end}}
     <div class="editor-toolbar">
         <button type="button" class="btn btn-tool" data-action="undo" title="Undo">↶</button>

assets/page/sections.js

@@ -4,13 +4,18 @@
     var headings = content.querySelectorAll('h1, h2, h3, h4, h5, h6');
     if (!headings.length) return;
 
-    // Section 0 is pre-heading content, editable via full-page edit.
-    // Sections 1..N each start at a heading; that is the index sent to the server.
-    // Skip headings that already carry a server-rendered edit link.
     headings.forEach(function (h, i) {
         if (h.querySelector('a.btn')) return;
         var a = document.createElement('a');
-        a.href = '?edit&section=' + (i + 1);
+
+        if (h.tagName === 'H1') {
+          a.href = '?edit';
+        } else if (h.tagName === 'H2') {
+          a.href = '?edit&section=' + (i + 1) + '&span';
+        } else {
+          return;
+        }
+
         a.className = 'btn btn-small btn-float';
         a.textContent = 'edit';
         h.appendChild(document.createTextNode(' '))

diary.go

@@ -10,7 +10,6 @@ import (
 	"os"
 	"path"
 	"path/filepath"
-	"regexp"
 	"sort"
 	"strconv"
 	"strings"
@@ -208,22 +207,6 @@ func findDiaryContext(root, fsPath, urlPath string) (depth int, diaryRootFS, dia
 	return 0, "", "", false
 }
 
-// headingTextRe matches an ATX heading at the start of a section. The
-// heading text is everything after the `#`s and the required space, on the
-// first line.
-var headingTextRe = regexp.MustCompile(`^(#{1,6})\s+([^\n]*)`)
-
-// sectionHeading returns the heading level (1..6) and trimmed text of a
-// section produced by splitSections. Returns level=0 for the pre-heading
-// section (index 0).
-func sectionHeading(section []byte) (level int, text string) {
-	m := headingTextRe.FindSubmatch(section)
-	if m == nil {
-		return 0, ""
-	}
-	return len(m[1]), strings.TrimSpace(string(m[2]))
-}
-
 // findSectionIndex returns the absolute section index whose heading text
 // matches target (e.g. "2026-05" or "2026-05-28"). Returns the first match.
 func findSectionIndex(sections [][]byte, target string) (int, bool) {

main.go

@@ -261,6 +261,7 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 	// Determine section index (-1 = whole page).
 	sectionIndex := -1
 	insertBefore := -1
+	sectionSpan := false
 	if editMode {
 		if s := r.URL.Query().Get("section"); s != "" {
 			if n, err := strconv.Atoi(s); err == nil && n >= 0 {
@@ -272,6 +273,7 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 				insertBefore = n
 			}
 		}
+		sectionSpan = r.URL.Query().Has("span")
 	}
 
 	var special *specialPage
@@ -323,7 +325,11 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 	} else if editMode && sectionIndex >= 0 {
 		sections := splitSections(rawMD)
 		if sectionIndex < len(sections) {
-			rawContent = string(sections[sectionIndex])
+			end := sectionIndex + 1
+			if sectionSpan {
+				end = secionSpanEnd(sections, sectionIndex)
+			}
+			rawContent = string(joinSections(sections[sectionIndex:end]))
 		}
 	} else if editMode && rawContent == "" && urlPath != "/" {
 		rawContent = "# " + pageTitle(urlPath) + "\n\n"
@@ -336,6 +342,7 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 		IsRoot:         urlPath == "/",
 		SectionIndex:   sectionIndex,
 		InsertBefore:   insertBefore,
+		Span:           sectionSpan,
 		PostURL:        urlPath,
 		RawContent:     rawContent,
 		Content:        rendered,
@@ -390,11 +397,7 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 	indexPath := filepath.Join(fsPath, "index.md")
 	redirectTarget := urlPath
 
-	// insert_before splices a new section into the file *at* index N rather
+	// handle section saving
-	// than replacing index N (used by the diary "create new day" flow).
-	// section replaces the section at index N (used by per-section edits).
-	// Exactly one of insert_before / section should be set; insert_before
-	// wins if both are present.
 	if s := r.FormValue("insert_before"); s != "" {
 		insertIndex, err := strconv.Atoi(s)
 		if err != nil || insertIndex < 0 {
@@ -431,8 +434,18 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 			http.Error(w, "section no longer exists — the page changed since you opened the editor", http.StatusConflict)
 			return
 		}
-		sections[sectionIndex] = []byte(content)
+
-		content = string(joinSections(sections))
+		// handling of section editing that spans until the next heading of the same level
+		end := sectionIndex + 1
+		if r.FormValue("span") != "" {
+			end = secionSpanEnd(sections, sectionIndex)
+		}
+		merged := make([][]byte, 0, len(sections)-(end-sectionIndex)+1)
+		merged = append(merged, sections[:sectionIndex]...)
+		merged = append(merged, []byte(content))
+		merged = append(merged, sections[end:]...)
+		content = string(joinSections(merged))
+
 		// Section index ≥ 1 is a heading-anchored section. Redirect to its
 		// anchor so the user lands on the section they just saved, even if
 		// the heading text changed.

render.go

@@ -52,6 +52,7 @@ type pageData struct {
 	IsRoot         bool
 	SectionIndex   int // -1 = whole page; >=0 = section being edited
 	InsertBefore   int // -1 = no insert; >=0 = splice new section at this index
+	Span           bool // causes section editing to also cover every sub-section to the next section of the same level
 	PostURL        string
 	RawContent     string
 	Content        template.HTML

sections.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"regexp"
+	"strings"
 
 	"github.com/yuin/goldmark/ast"
 	"github.com/yuin/goldmark/text"
@@ -10,6 +11,11 @@ import (
 
 var sectionHeadingRe = regexp.MustCompile(`(?m)^#{1,6} `)
 
+// headingTextRe matches an ATX heading at the start of a section. The
+// heading text is everything after the `#`s and the required space, on the
+// first line.
+var headingTextRe = regexp.MustCompile(`^(#{1,6})\s+([^\n]*)`)
+
 // splitSections splits raw markdown into sections.
 // Section 0 is any content before the first heading.
 // Each subsequent section begins at a heading line and runs to the next.
@@ -64,3 +70,31 @@ func joinSections(sections [][]byte) []byte {
 	}
 	return buf.Bytes()
 }
+
+// sectionHeading returns the heading level (1..6) and trimmed text of a
+// section produced by splitSections. Returns level=0 for the pre-heading
+// section (index 0).
+func sectionHeading(section []byte) (level int, text string) {
+	m := headingTextRe.FindSubmatch(section)
+	if m == nil {
+		return 0, ""
+	}
+	return len(m[1]), strings.TrimSpace(string(m[2]))
+}
+
+// sectionSpanEnd returns the exclusive end index of the section span starting
+// at start: the first following section whose heading level is <= start's.
+// Sections nested deeper than start (its subsections) belong to the span, so
+// editing a `##` covers every `###`+ under it up to the next `##` or `#`.
+func secionSpanEnd(sections [][]byte, start int) int {
+	level, _ := sectionHeading(sections[start])
+	if level == 0 {
+		return start + 1
+	}
+	for i := start + 1; i <= len(sections); i++ {
+		if l, _ := sectionHeading(sections[i]); l > 0 && l <= level {
+			return i
+		}
+	}
+	return len(sections)
+}