1 file changed, 26 insertions, 2 deletions
diff --git a/custom/extensions/about-render.lua b/custom/extensions/about-render.lua
index c833c00..ecb2abe 100644
--- a/custom/extensions/about-render.lua
+++ b/custom/extensions/about-render.lua
@@ -33,8 +33,32 @@ local max_depth = 24
 local filename, chunks = "", {}
 
 
+-- Lua patterns backtrack, so "%s+$" costs the square of a run of spaces in
+-- the middle of a line. Finding each end directly stays linear.
 local function trim(text)
-	return (text:gsub("^%s+", ""):gsub("%s+$", ""))
+	local first = text:find("%S")
+	if first == nil then
+		return ""
+	end
+	local last = #text
+	while text:find("^%s", last) do
+		last = last - 1
+	end
+	return text:sub(first, last)
+end
+
+-- A heading may close with a run of hashes, which only counts as markup when
+-- a space comes before it, so "# C#" keeps its sharp.
+local function heading_text(title)
+	title = trim(title)
+	local last = #title
+	while last > 0 and title:sub(last, last) == "#" do
+		last = last - 1
+	end
+	if last == 0 or title:find("^%s", last) then
+		return trim(title:sub(1, last))
+	end
+	return title
 end
 
 -- Normalise CRLF and CR to newlines, then split. A trailing newline yields
@@ -332,7 +356,7 @@ if has_lpeg then
 				blocks[#blocks + 1] = {
 					kind = "heading",
 					level = #hashes,
-					kids = parse_inline((title:gsub("%s*#*%s*$", ""))),
+					kids = parse_inline(heading_text(title)),
 				}
 				i = i + 1
 			elseif break_line:match(line) then