use of the u element in problematic - it once meant "underline" but html5 brought it back as "unarticulated text". as a result, it validates in epub3 and html5, but raises a validation error in epub2
We should replace it with a span element with underline style.
Example error:
2023-12-29 19:00:26,322 CRITICAL #72540 ERROR(RSC-005): /export/sunsite/users/gutenbackend/cache/epub/72540/pg72540-images.epub/OEBPS/3189201508802989844_72540-h-3.htm.html(197,24): Error while parsing file: element "u" not allowed anywhere; expected the element end-tag, text or element "a", "abbr", "acronym", "address", "applet", "b", "bdo", "big", "blockquote", "br", "cite", "code", "del", "dfn", "div", "dl", "em", "h1", "h2", "h3", "h4", "h5", "h6", "hr", "i", "iframe", "img", "ins", "kbd", "map", "noscript", "ns:svg", "object", "ol", "p", "pre", "q", "samp", "script", "small", "span", "strong", "sub", "sup", "table", "tt", "ul" or "var" (with xmlns:ns="http://www.w3.org/2000/svg")
ERROR(RSC-005): /export/sunsite/users/gutenbackend/cache/epub/72540/pg72540-images.epub/OEBPS/3189201508802989844_72540-h-3.htm.html(233,24): Error while parsing file: element "u" not allowed anywhere; expected the element end-tag, text or element "a", "abbr", "acronym", "address", "applet", "b", "bdo", "big", "blockquote", "br", "cite", "code", "del", "dfn", "div", "dl", "em", "h1", "h2", "h3", "h4", "h5", "h6", "hr", "i", "iframe", "img", "ins", "kbd", "map", "noscript", "ns:svg", "object", "ol", "p", "pre", "q", "samp", "script", "small", "span", "strong", "sub", "sup", "table", "tt", "ul" or "var" (with xmlns:ns="http://www.w3.org/2000/svg")
ERROR(RSC-005): /export/sunsite/users/gutenbackend/cache/epub/72540/pg72540-images.epub/OEBPS/3189201508802989844_72540-h-3.htm.html(261,24): Error while parsing file: element "u" not allowed anywhere; expected the element end-tag, text or element "a", "abbr", "acronym", "address", "applet", "b", "bdo", "big", "blockquote", "br", "cite", "code", "del", "dfn", "div", "dl", "em", "h1", "h2", "h3", "h4", "h5", "h6", "hr", "i", "iframe", "img", "ins", "kbd", "map", "noscript", "ns:svg", "object", "ol", "p", "pre", "q", "samp", "script", "small", "span", "strong", "sub", "sup", "table", "tt", "ul" or "var" (with xmlns:ns="http://www.w3.org/2000/svg")
ERROR(RSC-005): /export/sunsite/users/gutenbackend/cache/epub/72540/pg72540-images.epub/OEBPS/3189201508802989844_72540-h-3.htm.html(284,24): Error while parsing file: element "u" not allowed anywhere; expected the element end-tag, text or element "a", "abbr", "acronym", "address", "applet", "b", "bdo", "big", "blockquote", "br", "cite", "code", "del", "dfn", "div", "dl", "em", "h1", "h2", "h3", "h4", "h5", "h6", "hr", "i", "iframe", "img", "ins", "kbd", "map", "noscript", "ns:svg", "object", "ol", "p", "pre", "q", "samp", "script", "small", "span", "strong", "sub", "sup", "table", "tt", "ul" or "var" (with xmlns:ns="http://www.w3.org/2000/svg")
use of the u element in problematic - it once meant "underline" but html5 brought it back as "unarticulated text". as a result, it validates in epub3 and html5, but raises a validation error in epub2
We should replace it with a span element with underline style.
Example error: