{not available when compiled without the |+quickfix| feature} Name of the errorfile for the |:make| command (see |:make_makeprg|) and the |:grep| command. When it is empty, an internally generated temp file will be used. When "##" is included, it is replaced by a number to make the name unique. This makes sure that the ":make" command doesn't overwrite an existing file. NOT used for the ":cf" command. See 'errorfile' for that. Environment variables are expanded |:set_env|. See |option-backslash| about including spaces and backslashes. This option cannot be set from a |modeline| or in the |sandbox|, for security reasons.