Allow definition source to include modifications

[ccameron-chromium]

In SMPTE ST 2094-50, we want to include a modified source for a definition. Something to the effect of:

[SOURCE: ISO/DIS 21496-1:2025, modified — Notes 1, 2, and 3 to entry have been added.]

The code to insert the SOURCE part is here

html-pub/smpte.js

Line 1388 in dca1e12

element.insertBefore(document.createTextNode("[SOURCE: "), anchor);

I think that the easiest way to go about this would be to support code of the form:

   <dd><a href="#bib-iso-21496-1" data-mod="Notes 1, 2, and 3 to entry have been added"><a></dd>

In the code, if the data-mod attribute is present then we'd add the text =", modified -- ", appended by the text of the modification, followed by the close-bracket.

[SteveLLamb]

The tooling already allows for a note to entry as mentioned at https://doc.smpte-doc.org/html-pub/main/#sec-terms-definitions-clause. You can easily do what you need with using the example modified as you need:

<dt><dfn>term</dfn></dt>
<dd>definition.</dd>
<dd><a href="#bib-iso-21496-1"></a></dd>
<dd class="note">modified — Notes 1, 2, and 3 to entry have been added</dd>

And you can add as many note <dd> elements as you need.