IS_SUBDIR is subdir a subdirectory of dir?
canonicalization and normalization are NOT performed duplicated slashes are dropped
function s = is_subdir(subdir, dir) arguments subdir {mustBeTextScalar} dir {mustBeTextScalar} end s = stdlib.drop_slash(subdir); d = stdlib.drop_slash(dir); s = startsWith(s, d) && (strlength(s) > strlength(d)); end