This was introduced in 38b5393 (Nov 10 2004), in support of the now defunct GTK backend for supporting separable tweaks.
https://codereview.appspot.com/551380043
Diff:
Passes make, make check and a full make doc.
Patch on countdown for January 25th
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Issue 5673: Remove implicit evaluation of the ".twy" file master staging author Han-Wen Nienhuys <hanwen@lilypond.org> Sat, 25 Jan 2020 13:32:27 +0000 (14:32 +0100) committer David Kastrup <dak@gnu.org> Sat, 25 Jan 2020 13:32:27 +0000 (14:32 +0100) commit c5ffa540fdbe52486b9575567ede70be575adb47
Diff:
Passes make, make check and a full make doc.
Patch on countdown for January 25th
Patch counted down - Please Push.