Unfortunately, there is not an addon (plugin) of the WP tinymce which provides the anchor functionality. Instead, it is part of the tiny_mce.js
file WP uses in it’s ‘includes’ directory.
That file is a monster… but if you unminify it.. you will notice two instances where the anchor element is defined.
One looks like this (around line 544 unminified):
if (b.anchor) {
f += "#" + b.anchor
}
return f
And the other, like this (around line 659 unminified):
if (b.anchor) {
c += "#" + b.anchor
}
b.source = c
I’m not sure the effect of changing these two to include the id attribute.. but I’m sure you will figure it out 😉
Tinymce Advanced doesn’t have anything to do with it except telling the main WP js file to include that button (and it’s functionality).
As far as a filter to modify the anchor element from WP… I haven’t seen one in my experience.