Check requirement to have EOF/BOF versus {X-Y} at the beginning of a sequence

[ross-spencer]

Doing something weird with this in the conversion (I think because one worked over the other, or we need to check if one is more inclusive than the other), e.g. https://github.com/ffdev-info/simpledroid/blob/5679056ee6266eaa188e6f9806c3477a6b2761a1/reference/DROID_SignatureFile_Simple_2024-11-11T12-29-22Z.xml#L59 which is https://www.nationalarchives.gov.uk/PRONOM/fmt/1570