.l5 {background: #EFD} /* yes, supported, ubiquitous, native */
/* default u-ascii */
.l6 {background: #DFD} /* complete, perfect */
+.l9 {background: #EEE} /* unknown, omitted */
.ex {background: #EEE} /* experimental, disfavoured */
.u-invalid {background: #BBB} /* invalid, impossible */