docs: def ligolw_add(xmldoc, urls, non_lsc_tables_ok = False, verbose = False, contenthandler = DefaultContentHandler):
  	"""
  	An implementation of the LIGO LW add algorithm.  urls is a list of
  	URLs (or filenames) to load, xmldoc is the XML document tree to
  	which they should be added.
  	"""
  	# Input
  	for n, url in enumerate(urls):
  		if verbose:
  			print >>sys.stderr, "%d/%d:" % (n + 1, len(urls)),
  		utils.load_url(url, verbose = verbose, xmldoc = xmldoc, contenthandler = contenthandler)
  
  	# ID reassignment
  	if not non_lsc_tables_ok and lsctables.HasNonLSCTables(xmldoc):
  		raise ValueError("non-LSC tables found.  Use --non-lsc-tables-ok to force")
  	reassign_ids(xmldoc, verbose = verbose)
  
  	# Document merge
  	if verbose:
  		print >>sys.stderr, "merging elements ..."
  	merge_ligolws(xmldoc)
  	merge_compatible_tables(xmldoc)
  
  	return xmldoc