Document the Wikidata node syntax with source.
@@ -578,6 +578,10 @@ class KgtkValue(KgtkFormat):
si_combiner=si_combiner_pat,
si_power=si_power_pat)
# Wikidata nodes (for units):
+ #
+ # https://www.wikidata.org/wiki/Wikidata:Identifiers
+ #
+ # "Each Wikidata entity is identified by an entity ID, which is a number prefixed by a letter."
nonzero_digit_pat: str = r'[1-9]'
wikidata_node_pat: str = r'(?P<wikidata_node>Q{nonzero_digit}{digit}*)'.format(nonzero_digit=nonzero_digit_pat,
digit=digit_pat)
