Valid HTML5 <p> tag within <a> tags causes a crtical error

[rtonsing]

This usage: <a href="music/p0021.mxl"><p class="center">[mxl]</p></a> results in a critical error:

CRITICAL:root:validation error reported by EPUB_VALIDATOR:
CRITICAL:root:ERROR(RSC-005): /htdocs/ebookmaker/cache/20260805093040/10001-epub.epub/10001/1501810647186941550_aesthetik_der_tonkunst-7.html.html(379,79): Error while parsing file: element "p" not allowed here; expected the element end-tag, text or element "a", "abbr", "acronym", "applet", "b", "bdo", "big", "br", "cite", "code", "del", "dfn", "em", "i", "iframe", "img", "ins", "kbd", "map", "noscript", "ns:svg", "object", "q", "samp", "script", "small", "span", "strong", "sub", "sup", "tt" or "var" (with xmlns:ns="http://www.w3.org/2000/svg")

but it is valid HTML5, and passes the Nu validator. Changing it to <p class="center"><a href="music/p0021.mxl">[mxl]</a></p> prevents the error.

Aesthetik_der_Tonkunst_upload-orig.zip

output.txt

[eshellman]

turns out it's not valid xhtml - has nothing to do with the music. similarly, div is not allowed in a