Currently, on a abusefilter edit page, there are two ways to make comments.

1. A free text box (below the code box), which can be used to explain the filter goal; to explain how the filter works; and also to list all major changes to the filter (with date, name of the editor and comment), as we would do with edit summaries in an article history.
2. We can also insert comments inside the code in the upper box, with the syntax: /* */

In a lot of cases, this is not convenient. When doing maintenance, especially on large filters, we need to read comments in order to know if a specific part of a filter is still needed or is obsolete. (1) Finding the corresponding comment in the free text box is a chore on big filters or filters with long history; (2) if there is an inline comment, it's obviously a lot easier, but too long inlines comments complexifies the code reading.

Proposed solution: Keep the free text box (for global comments). Separate the filter code box in two horizontaly, with on the left side the filter code, on the right side a comment box line by line (each line of code has a corresponding line of comment), see picture below. It would make the comments a lot easier to find (1) while keeping the code clean (2). For a good UX, this requires T294856 (larger and resizable window).