td.di-d {background: #FFD} /* rfc-1345 digraph */
td.di-prop {background: #FED} /* proposed digraph */
td.di-a {background: #EFD} /* ascii */
+td.di-aa {background: #DFD} /* ascii */
td.di-rare {background: #EEE} /* disfavoured */
td.di-invalid {background: #BBB} /* impossible */
td.di-d:hover {background: #FF8}
td.di-prop:hover {background: #FC8}
td.di-a:hover {background: #CF8}
+td.di-aa:hover {background: #8F8}
/* key type colorization */