Ok, so after some more thought I've slightly changed my mind on how I think we should handle this. My suggestion...
We should have two separate tags:
page-layout
This would then be used, much as it is now, for questions about composition and layout in the context of desktop publishing and the design of "pages" (which doesn't actually have to be a physical "page" at all... a web page for example completely fits here).
And then anything about "layout" in the more general sense should be tagged...
composition
Composition relates more broadly to the placement and arrangement of elements. So questions about cropping images, the placing of elements within an image, the arrangement of elements in an animation or illustration, etc. are more appropriate here.
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The layout tag should then be merged in to and made a synonym of composition. The rationale being that 'layout' is much broader in general language and when not being used as a contraction of 'page layout' is more synonymous with 'composition'.
'Composition' is a broader term that is still perfectly appropriate for questions about page layout, so there's no harm in questions about page layout being tagged 'composition'... whereas if we made 'layout' a synonym of 'page-layout' (or the other way around), we would end up with questions about, e.g. arranging elements in an illustration, tagged 'page-layout'.
The tag wikis for both tags would need be updated to reflect and explain this distinction.
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It's worth noting that there are also compositions in After Effects, which composition is currently used for on a few questions... I'm not sure if there needs to be another tag for that or if can just be removed from those questions?