@NotNull
    private String getIndexNumberText() {
        final ASTNode node = getNode().findChildByType(RegExpTT.NUMBER);
        if (node != null) {
            return node.getText();
        }
        final String s = getUnescapedText();
        boolean pcreBackReference = s.charAt(1) == 'g';
        boolean pcreNumberedGroup = s.startsWith("(?");
        assert s.charAt(0) == '\\' || pcreNumberedGroup;
        return pcreBackReference ? getPcreBackrefIndexNumberText(s.substring(2)) :
               pcreNumberedGroup ? getPcreNumberedGroupIndexNumberText(s.substring(2)) :
               s.substring(1);
    }
@NotNull
    private String getIndexNumberText()