import re


def extract_refseq_accession_id(seqIdString):
    """
    Extract the RefSeq accession number in the description string.
    
    See: https://www.ncbi.nlm.nih.gov/books/NBK21091/table/ch18.T.refseq_accession_numbers_and_mole/?report=objectonly
    See: http://www.ncbi.nlm.nih.gov/books/NBK50679/#RefSeqFAQ.what_are_the_distinguishing_fe
    """
    seqId = ''
    regex1 = re.compile(r'(\s|\||^)([A-Z]{2}_[0-9.]+)(\s|\||$)')
    seqIdSearch = re.search(regex1, seqIdString)
    if seqIdSearch:
        seqId = seqIdSearch.group(2)
    return seqId