Escaped question marks in the replace function match between characters

[Alzarath]

For context, I was attempting to match Youtube URLs with the query string e.g. watch?v=... which of course required me to escape the question mark.

I'm not very familiar with re2, but from what I can tell searching for an escaped question mark (\?) does not function as intended. At least, this is the case for the replace rewrite rule.

Effect: Using the rewrite rule replace("\?"|"A") will add the letter A between every character.

Expected: Using the rewrite rule replace("\?"|"A") will replace all question marks with the letter A.

Additionally, including \? seems to break the whole search string, causing the same issue as above. For example, if I used replace("watch\?v=(.*?)\""|"A"), it will still add an A between every character.

I've tried using my regex on Regex Planet to be sure I was getting the right results otherwise and that was successful.

For completeness sake, I tried replace("?"|"A") and it had no effect on the content.

I know there are more contexts to use regex, but it's already taken me hours to identify and replicate this as is, but I imagine it applies to those contexts as well.

[Alzarath]

I've done less testing on it, but it appears that escaping a period (\.) has similar behavior.

[Alzarath]

I've done some more testing after considering things and realized that escaping these regex-specific characters works when double-escaping (e.g. \\., \\?) the characters.

It may seem obvious in hindsight, but the reason I never considered it was because I needed to escape quotation marks (\") to include them in the regex search, which is done with a single backslash, and can not be done with a double backslash.

This revelation changes the context of the issue in a way that I might need to reconsider it as a whole. Does something need to be done about this, whether it be in changing something or just documenting the somewhat unintuitive distinction?