I have this piece of html from wikipedia.
<a href=3D"https://en.wikipedia.org/wiki/Judith_Ehrlich" title=3D"Judith Ehrlich">Judith Ehrlich</a>
I understand "=3D" is Quoted-Printable encoding for "=" but im not sure what 3D"URL" means. Normally when I would see a link in HTML it would be written like this
<a href="https://en.wikipedia.org/wiki/Judith_Ehrlich" title="Judith Ehrlich">Judith Ehrlich</a>
In quoted-printable, any non-standard octets are represented as an = sign followed by two hex digits representing the octet's value. To represent a plain =, it needs to be represented using quoted-printable encoding too: 3D are the hex digits corresponding to ='s ASCII value (61).
In other words, the sequence of =3D"URL" in those fields is converted to just ="URL". 3D"URL" without = has no meaning on its own.
If used in a parsing/rendering situation that is interpreting = as a QP encoding, omitting 3D would result in the parser wrongly interpreting the next characters (e.g. "U) as a byte encoding. Using =3D would be necessary to insert an actual = in the parsed result.