Constructing a URI in the format X123$45 as the link target of line number 45 in the line number column of document X123 (resp. X123$1-10 for lines 1-10) provides the ability to highlight one or several lines, and accessing this URI highlights the corresponding lines and automatically scrolls to the highlight line(s) with 60px top margin.

The downside of using this custom JS-based approach instead of standard # HTML anchor fragments is that every URI linked from the line number column in Pastes and Diffusion file pages is semantically a separate URI to crawl (due to $ instead of # as a fragment separator).

As a compromise,

• use standard # for the link target of each single line and when highlighting a single line. This makes us lose line highlighting and vastly reduces the number of links a crawler could follow when indexing a Paste or Diffusion file page,
• keep using custom $ when explicitly highlighting multiple lines.

See T15670

• Go to http://phorge.localhost/P1, click on line number 11, see that highlighting still works and URL in the address bar becomes http://phorge.localhost/P1#11 without a page reload
• Access URL http://phorge.localhost/P1#13 and see that position scrolling by the browser works as expected (but no line highlighting)
• Go to http://phorge.localhost/P1, click on line number 11 and drag to number 17, see that highlighting still works and URL in the address bar becomes http://phorge.localhost/P1$11-17
• Access URL http://phorge.localhost/P1$9-16 and see that highlighting and position scrolling by the server-side JS still works as expected
• Perform the same tests in a source code file rendered in Diffusion