Automatic summary may generate invalid HTML with blockquotes and lists #14044
Description
What version of Hugo are you using (hugo version)?
$ hugo version hugo v0.151.0+extended+withdeploy darwin/arm64 BuildDate=2025-10-02T13:30:36Z VendorInfo=brew
Does this issue reproduce with the latest release?
Yes
Issue
Using a blockquote that extends past the .Summary cutoff causes the content below {{ .Summary }} to be treated as part of the blockquote until the end of the parent tag. Reproduction repo
Hugo's .Summary may lead to blockquote end tag be below cutoff point
Explanation
In most modern browsers this html code will be parsed and rendered without errors
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
</head>
<body>
<main>
<blockquote>
<p>1</p>
</main>
</body>
</html>Leading to shown in browser as a source
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
</head>
<body>
<main>
<blockquote>
<p>1</p>
<!-- This blockquote end tag was automatically inserted -->
</blockquote>
</main>
</body>
</html>This is due to these parsing rules
An end tag whose tag name is one of: "address", "article", "aside", "blockquote", "button", "center", "details", "dialog", "dir", "div", "dl", "fieldset", "figcaption", "figure", "footer", "header", "hgroup", "listing", "main", "menu", "nav", "ol", "pre", "search", "section", "select", "summary", "ul"
If the stack of open elements does not have an element in scope that is an HTML element with the same tag name as that of the token, then this is a parse error; ignore the token. Otherwise, run these steps: Generate implied end tags. If the current node is not an HTML element with the same tag name as that of the token, then this is a parse error. Pop elements from the stack of open elements until an HTML element with the same tag name as the token has been popped from the stack.
To Discuss
I think the best case scenario is for .Summary to handle generation of implied tags. But I am not sure how to do that myself.
For now I plan to provide a PR with fixes for a theme and docs, to avoid confusion and errors