multiline environment (with tags) rendering issues
(This came up while testing 2.7.4 but is also present in 2.7.3 and probably ealier.)
I ran into 2-3 issues around multline; I'm not sure how to split them.
Minimal example:
$$\begin{multline}xxxxxxxxxx\tag{1} \\ yyyyyyyyyy\end{multline}$$(default) equation label alignment
IIUC, the equation label should align with the first line of the expression.
However, with its default (labels on right), the label aligns with the second line; furthermore, using the CommonHTML output the row overlaps the label (SVG and HTML-CSS are fine).
This matches toMathML which has the label in the second row / mlabeledtr.
left-aligned equation labels
When equation labels are left-aligned, both SVG and CommonHTML align the label at the first row. (I didn't check HTML-CSS).
SVG with small container size
If the container size is small (e.g., 0), the SVG output renders poorly (and differently from CommonHTML; I didn't check HTML-CSS): the second row ends below the beginning of the first row (excluding the left-aligned label).
Sample output (via mathjax-node with width:0 but happens in the client as well):
<svg xmlns:xlink="http://www.w3.org/1999/xlink" width="20.75ex" height="6.259ex" style="vertical-align: -2.531ex; margin-left: -5.832ex; margin-right: -10.352ex;" viewBox="-2511.1 -1605.1 8934 2695" role="img" focusable="false" xmlns="http://www.w3.org/2000/svg" aria-labelledby="MathJax-SVG-1-Title">
<title id="MathJax-SVG-1-Title">\begin{multline} xxxxxxxxxx \tag{1}\\ yyyyyyyyyy \end{multline}</title>
<defs aria-hidden="true">
<path stroke-width="0" id="E1-STIXWEBMAIN-28" d="M304 -161l-12 -16c-158 90 -244 259 -244 429c0 185 87 329 247 424l9 -16c-139 -119 -170 -212 -170 -405c0 -186 30 -299 170 -416Z"></path>
<path stroke-width="0" id="E1-STIXWEBMAIN-31" d="M394 0h-276v15c74 4 95 25 95 80v449c0 34 -9 49 -30 49c-10 0 -27 -5 -45 -12l-27 -10v14l179 91l9 -3v-597c0 -43 20 -61 95 -61v-15Z"></path>
<path stroke-width="0" id="E1-STIXWEBMAIN-29" d="M29 660l12 16c153 -92 244 -259 244 -429c0 -185 -88 -327 -247 -424l-9 16c142 117 170 211 170 405c0 187 -25 302 -170 416Z"></path>
<path stroke-width="0" id="E1-STIXWEBMAINI-78" d="M243 355l12 -57c70 107 107 143 151 143c24 0 41 -15 41 -37c0 -21 -14 -36 -34 -36c-19 0 -28 17 -52 17c-18 0 -54 -44 -98 -121c0 -7 2 -21 8 -45l32 -134c7 -28 16 -41 30 -41c13 0 24 10 47 40c9 12 13 18 21 28l15 -9c-58 -90 -84 -114 -122 -114 c-32 0 -47 18 -59 68l-29 119l-88 -119c-44 -59 -64 -68 -95 -68s-50 16 -50 42c0 20 14 36 34 36c9 0 19 -4 32 -11c10 -6 20 -9 26 -9c11 0 30 19 51 49l82 116l-28 124c-14 60 -21 68 -46 68c-8 0 -20 -2 -39 -7l-18 -5l-3 16l11 4c61 22 94 29 117 29 c25 0 37 -18 51 -86Z"></path>
<path stroke-width="0" id="E1-STIXWEBMAINI-79" d="M243 186l21 -110c85 141 122 213 122 257c0 14 -7 20 -26 32c-20 13 -26 23 -26 39c0 22 17 37 40 37c30 0 52 -25 52 -55c0 -57 -48 -167 -131 -305c-104 -172 -211 -287 -268 -287c-30 0 -51 17 -51 43c0 22 17 40 39 40c35 0 35 -28 61 -28c13 0 25 8 48 33 c18 19 63 78 71 91c6 12 10 24 10 35c0 40 -55 264 -82 332c-19 49 -37 64 -77 64c-11 0 -20 -1 -31 -4v17c11 2 22 4 32 6c20 4 53 10 107 18h4c15 0 68 -166 85 -255Z"></path>
</defs>
<g stroke="currentColor" fill="currentColor" stroke-width="0" transform="matrix(1 0 0 -1 0 0)" aria-hidden="true">
<g id="mjx-eqn-1" transform="translate(0,703)">
<use xlink:href="#E1-STIXWEBMAIN-28"></use>
<use xlink:href="#E1-STIXWEBMAIN-31" x="333" y="0"></use>
<use xlink:href="#E1-STIXWEBMAIN-29" x="833" y="0"></use>
</g>
<g transform="translate(1966,0)">
<g transform="translate(-14,0)">
<g transform="translate(0,703)">
<use xlink:href="#E1-STIXWEBMAINI-78" x="0" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="447" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="894" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="1341" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="1788" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="2235" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="2682" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="3129" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="3576" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-78" x="4023" y="0"></use>
</g>
<g transform="translate(-4440,-797)">
<use xlink:href="#E1-STIXWEBMAINI-79" x="0" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="444" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="888" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="1332" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="1776" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="2220" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="2664" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="3108" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="3552" y="0"></use>
<use xlink:href="#E1-STIXWEBMAINI-79" x="3996" y="0"></use>
</g>
</g>
</g>
</g>
</svg>