Emulating regexp lookarounds in GNU sed

This stackoverflow Q&A got me thinking about various ways to construct a solution in GNU sed if lookarounds are needed.

info Only single line (with newline as the line separator) processing is presented here. Equivalent lookaround syntax with grep -P or perl is also shown for comparison. Cases where multiple lines and/or ASCII NUL characters are present in the pattern space is left as an exercise.

Search and replace tricks with ripgrep

ripgrep (command name rg) is a grep tool, but supports search and replace as well. rg is far from a like-for-like alternate for sed, but it has nifty features like multiline replacement, fixed string matching, PCRE2 support, etc. This post gives an overview of syntax for substitution and highlights some of the cases where rg is a handy replacement for sed.