Broken anchor links for headings with special characters in their ids

[mcmd]

Description of the issue found on ampproject.org

Please provide:

• Page link: https://amp.dev/documentation/examples/guides/internationalization/
• Description of the documentation issue

The anchor links on the ToC on the right side do not work.

For instance, for the Last link ("Example 2: Canonical + Alternate + AMP"), the link is:
https://amp.dev/documentation/examples/guides/internationalization/?referrer=ampbyexample.com#example-2-canonical-alternate-amp

But it should be:
https://amp.dev/documentation/examples/guides/internationalization/?referrer=ampbyexample.com#example-2:-canonical-+-alternate-+-amp

How do we reproduce the issue?

Please provide the steps to reproduce the issue:

1. Navigate to the Internationalization page
2. Click on "Example 2: Canonical + Alternate + AMP" in the Table of Contents
3. Link doesn't work

What browser are you using? Version 73.0.3683.103 (Official Build) (64-bit)
What O/S are you using? macOS 10.13.6 (17G6030)

[mcmd]

This iis happening also in the Using the Google AMP Cache article, with the "Redirect & Error Handling" Element in the ToC. It seems like there is a mismatch between the id of the elements in the page and the anchor link used in the ToC when there are special characters ('&' in this particular case, ':' in the original post)

A third example (also with a '&' in the id of the element) would be in the Product Browse Page article, with the "Offers & highlights" link in the ToC

[mcmd]

Changing title to "Broken anchor links for headings with special characters in their ids" as this seems to be a site-wide issue with the generation of the anchor links when the headings's ids contain special characters.