will be converted to a long string by joining stringified atoms using single spaces. then will be searched for %s placeholders, which will be replaced by arguments \$1, \$2, \$3, etc., sprintf style. (supports several %s unlike [makefilename]). make error messages on behalf of the containing abstraction instance in the case of a toplevel patch like this (non-abstraction) the error message will contain "[???]" list of arguments for substituting into the %s placeholders. after substitution is done, an error message will be generated with that text. the apparent source of the error will be the abstraction instance containing [gf/error], if applicable. this is what Find Last Error will find and highlight. generate an error on behave of a higher abstraction. \$1 is how many instances to climb up (NOT how many canvases). then \$1 is shifted out, as the rest of the arguments are used as in list (list \$2 \$3 \$4 ...)