One often needs clear indications of how a document has changed, but the commonest
technique, “change bars” (also known as “revision bars”), requires surprisingly much
trickery of the programmer (the problem being that TeX ‘proper’ doesn’t provide the
programmer with any information about the “current position” from which a putative
start- or end-point of a bar might be calculated; PDFTeX does provide the information,
but we’re not aware yet of any programmer taking advantage of the fact to write a
PDFTeX-based changebar package).
The simplest package that offers change
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