Clarification about regex "flavor"

Hi

The Calibre editor and Sigil offer to store your "saved searches". I know there are some small differences between them about the regex flavor being supported but I am unable to tell precisely which does what.

On the other hand there are also excellent sites for training and testing purposes like https://regex101.com/.

Is the latter compatible with either Sigil or Calibre? It offers (among several other flavors) a PCRE option.