The engine does not consider the possibility of using lookahead assertion in end of 'begin' attribute

[unreal666]

For example,

hljs.registerLanguage('mylang', function(hljs) {
    return {
        contains: [
            {
                className: 'class1',
                begin: /^a(?!bc)/,
            },
            {
                className: 'class2',
                begin: /^[^\r\n]/,
            }
        ]
    };

Testing string: 'abc'.
'a' char will match 'class1', although it should 'class2'.

For 'end' attribute - same.

[joshgoebel]

Closing this as a dup. Progress on this is tracked with this issue:

#1349