Basically, symbolic names are not implemented and result in a NumberFormatException. Attached is a patch which aligns implementation with the documentation along with doc updates and unit tests.
Created attachment 34472 [details] Patch for aligning the implementation to the documentation
The patch is based on mod_rewrite.c code https://github.com/apache/httpd/blob/fbc5e20ead005fd3a2bec05924f9e90dfd195406/modules/mappers/mod_rewrite.c#L3668-L3681
Thanks for the report and the patch. Fixed in: - trunk for 9.0.0.M14 onwards - 8.5.x for 8.5.9 onwards - 8.0.x for 8.0.40 onwards 7.0.x and earlier are not affected as the RewriteValve is not present in those versions. The patch was applied with some minor changes to replaces tabs with 4 spaces and to align formatting with the existing code.