3 backslashes work as well according to
https://stackoverflow.com/a/28063081
However, it might be confusing as the behaviour would change in double qouted strings. Also mw-core seems to mostly use 4 backslashes.
https: //codesearch.wmcloud.org/core/?q=%5B%5E%5C%5C%5D%5C%5C%5C%5C%5C%5C%5B%5E%5C%5C%5D&i=nope&files=.php%24&excludeFiles=&repos=
Change-Id: I9be37c386f8ca0f9d0a7be641484654cf9a2f7fa
Texutil related functionalities and tests will come in other changeset.
Related code:
fb56991251/lib/nodes/
Bug: T312528
Change-Id: Iead338a31403348603442b43ae802270f6b1d675