FWIW, what got me confused was that, typing
filename space
into Help/Search
returns a bunch of stuff, including:
str maybe_quote_filename(_str filename)
Returns: _str
Returns filename, with quotes around it, if it contains a space character. Otherwise filename is returned.
which led me to leap to the conclusion that SE took care of that part of the problem.
mea culpa, mea culpa, mea maxima culpa.