+# returned list, or fill only specified info.
+#
+# Invalid projects are removed from the returned list if and only if you
+# ask 'age' or 'age_string' to be filled, because they are the only fields
+# that run unconditionally git command that requires repository, and
+# therefore do always check if project repository is invalid.
+#
+# USAGE:
+# * fill_project_list_info(\@project_list, 'descr_long', 'ctags')
+# ensures that 'descr_long' and 'ctags' fields are filled
+# * @project_list = fill_project_list_info(\@project_list)
+# ensures that all fields are filled (and invalid projects removed)
+#