Comment by maxerickson

The mentioned Overpass API uses sets as a sort of fundamental concept, so the code

    way[building][!name];foreach{(._;>;);out;}

can be replaced with

    way[building][!name];(._;>;);out;

The "(._;>;);" stanza is sort of dense and seems opaque without knowing what it's doing, but it's straightforward, returning the union "();" of the previous result "._;" and the children of the previous result ">;".

The change I propose above adjusts the ">;" to operate on all of the "way[building][!name];" results together, rather than each element one at the time.