You can't in the matchtext itself but you can with an if statement. Example:
on *:TEXT:*Chandler*was*seen*:#: {
; used regex because there is no ISWMCS :(
if ($regex($1-,Chandler.*was.*seen)) { msg #mychan $strip($1-) }
}
Perhaps a good feature suggestion would be a prefix for events that makes the matchtext case sensitive. ISWMCS has already been suggested.
pssst: close your code tag...