note Roy Johnson Generally, the decision about using <c>?:</c> is not about whether it's necessary, but that capturing whatever you're grouping <i>isn't</i> necessary. The <c>?:</c> modifier makes parentheses not capture, which is somewhat more efficient and might make the task of counting left parentheses less onerous. <p> By the way, it's not a lookaround feature. <!-- Node text goes above. Div tags should contain sig only --> <div class="pmsig"><div class="pmsig-300037"> <hr> <small><b>Caution:</b> Contents may have been coded under pressure.</small> </div></div> 518444 650210