Our help regarding String type and related functions (e.g., Mid) needs clarifications:
1. There's no mention that indexing of characters starts from 1. (This may be confusing, when users don't see the difference between UNO API, where normal is 0-based indexing, and BASIC functions.)
2. There are multiple mentions of "max characters is 65535". This is wrong; actually, strings may be as long as 2G characters.
Olivier Hallot committed a patch related to this issue.
It has been pushed to "master":
tdf#136213 Basic string functions update