Due to the issue in there is currently a difference between the results obtained from typing "term1 term2" vs. "term1 AND terms2" in the Any Field box of the Works Search or the header quick search box, while our help at https://archiveofourown.org/help/work-search-text-help.html says there is not.
Relevant section of current help text:
space: a space acts like AND
Harry Potter will find Harry Potter and Harry James Potter but not Harry.
New help text:
space: acts like AND for search terms in the same field of the work
Harry Potter will find Harry Potter or Harry James Potter in any field, but it won't find works by a creator named Harry with the character tag Sherman Potter
AND: searches for works which have both terms in any field
Harry AND Potter will find works by a creator named Harry with the character tag Sherman Potter