-# native and QEMU-emulated runners. The same source compiles against CUPS
-# 2.4.x, 2.5.x and 3.x; this script provides each of those CUPS builds, then
-# builds the dependency stack (pdfio, libcupsfilters, libppd) and finally
-# cups-filters itself against it.
+# native and QEMU-emulated runners. cups-filters is a CUPS 2.x compatibility
+# layer (classic filters), so it targets CUPS 2.4.x and 2.5.x only -- NOT
+# CUPS 3.x/libcups3, which has no filter-executable concept. This script
+# provides each CUPS build, then the dependency stack (pdfio, libcupsfilters,
+# libppd) and finally cups-filters itself against it.