The SPEC_FILTER make variable is meant to be used to create small documentation bundles that just contain some selected files. Example usage:

make docs-specs-zip SPEC_FILTER="%-jls.md copyright.html %logo.gif resources"

The fix for JDK-8349143 caused the feature to stop working: no matter what the filter variables says, all the specs get built. This is a regression, old behavior needs to be restored.