HTML export wraps headlines in anchor tags with IDs, so that they can be linked by suffixing #[anchor-tag-ID] to the URL.
HTML export used to use anchor IDs like "sec-2" for the second headline, but at some point it switched to generated IDs like "org7ffb324", which change on every re-export. This means anchor-links on external sites (that is, links which link to a specific section of an org file) break every time an org file is re-exported to HTML. The old style of anchor IDs would break URLs when sections moved around, but at least it wouldn't break on every re-export! This makes org much less useful for typical web publishing use cases. This can be worked around by setting CUSTOM_ID for every headline, which will override the anchor id used, but I think it was much better when it just worked by default... It looks like this was changed in commit 459033265295723cbfb0fccb3577acbfdc9d0285 "Export back-ends: Use `org-export-get-reference'" Perhaps this functionality (of generating anchor IDs based on the section number) could be added back in?
