I think this bible is an interesting attempt at avoiding call outs but... I agree with the parent - /\s(.?)\s/\1/ is just easier to read, even with character classes /[:space:](.?)[:space:]/\1/ than the trim example, it's actually a bit sad that string manipulation is the first section since string manipulation is such an inherently dirty task to do.

It is neat to discover functionality of bash I was unaware of by see folks push it to the limit though.