" failed " =~ /(?{ $ok = 1 })XXX/;
print $ok ? "Good" : "Bad";

##</code><code>##

Compiling REx `(?{ $ok = 1 })XXX'
size 5 Got 44 bytes for offset annotations.
first at 1
   1: EVAL(3)
   3: EXACT <XXX>(5)
   5: END(0)
anchored `XXX' at 0 (checking anchored) minlen 3 with eval
Offsets: [5]
        1[14] 0[0] 15[3] 0[0] 18[0]

##</code><code>##

Guessing start of match, REx `(?{ $ok = 1 })XXX' against ` failed '...
Did not find anchored substr `XXX'...
Match rejected by optimizer