+ * Call preprocessor hooks in void context during the scan pass. This allows
+ the hook to determine if it's just scanning, and avoid expensive
+ operations.
+ * img: Detect scan mode and avoid generating and writing the image file
+ during it, for a 2x speedup.
+ * meta: Run in scan mode again (more intelligently) and re-add support for
+ meta link.
+ * Fix support for the case where metadata appears after an inline directive.
+ This was broken in version 2.16.