- bring back intended behavior as in FC 0.19:
- if 2 lengths, then midplane is invisible
- if reversed checked, then no symmetric and if symmetric then no reverse
- unify the code for Pad and Pocket (reversed is always visible)
- fix a typo in a bool name
Used when finding subelements of a feature. Many of the comparisons used to also
check for string lengths, but as far as I can tell they are not strictly
necessary (see https://www.cplusplus.com/reference/string/string/substr/) and
just `substr` can be used without them. However, `compare` explicitly is for
comparing, and does not make a new object that `substr` does.
