I propose that the help node for the Search and Super Search facilities, Using the Simple Search, be updated to explicitly say what sort of search strings are allowed.
Empirically, I have found (single quotes here bracket the search expressions used)
'kvale' and 'kv' find my home node, but 'kva+le' does not. So exact words and and exact substrings are allowed, but regexes are apparently not.
'kv and ale' does not perform a proper conjunction, but 'kv && ale' does.
in the expression 'kv ale' the space represents an implied or between 'kv' and 'ale'
'! kvale' returns kvale as a node, so doesn't seem to work
' (kv && ale)' does not return my homenode, so grouping does not seem to work.