Some mapping probes have special flags set. These are flags that can be set, and then their presence/absence tested-for using the general mapping table facility of $:, $; tests. $:x causes an entry to match only if the flag x is set. $;x causes an entry to match only if the flag x is clear. See specific mapping table descriptions Table 10–2for any special flags that may apply for that table.
When the intention is that an entry should succeed and terminate if the flag check succeeds, but that the mapping process should continue if the flag check fails, then the entry should use the $C metacharacter to the left of the flag check and use the $E flag to the right of the flag check.