a ? means that the preceding character or group is optional - a ? is called a qualifier - so Sinhalese? mean that Sinhales and Sinhalese will match.
however ???? means that the ? quantifiers are applying to each other - nested in other words, and that is not allowed in Perl's regex implementation

In reply to Re: Error! Nested quantifiers in regex by leriksen
in thread Error! Nested quantifiers in regex by banduwgs

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