Extracts abbreviations which are preceded by the full text (e.g. 'The Quebec Xylophone Enterprise Foundation (QXEF)').
extract_validate_abbreviations(lines)Lines to extract
Character vector of abbreviations of the form (ABC)
Only 'valid' abbreviations are extracted, viz. those abbreviations of the form (ABC) where the first letters
of the preceding words
(excluding some common words like of, and, etc.) are 'a', 'b', 'c'.