Quickbuild not handling subpages #531
Description
Noticed this in #493 , where the readiness.ptx file is being changed. The quick build fails (although a full build succeeds), with the following error:
* PTX:ERROR: the element with the @xml:id given as a subtree root ("VE-intro") is not division that can be chunked into HTML page(s). Quitting...
I believe it is complaining because the root of this file is an <introduction> that is included into the main.ptx page. So perhaps what needs to happen is that any file with an <xi:include/> checks the included files for changes, and rebuilds if they are changed; and files whose root element is not a <chapter> or <section> or perhaps a few other limited exceptions are not built in the preview.