function main( context ) {
	/**
	* Checks whether function documentation starts with an alias signature.
	*
	* @private
	* @param {Object} ast - full AST
	*/
	function hasSignature( ast ) {
		var signature = ast.signature;
		if ( !signature ) {
			context.report( 'REPL documentation must start with an alias signature', ast );
		}
		if ( ast.idx === 0 && !startsWith( signature.raw, '{{alias}}' ) ) {
			context.report( 'First function signature must start with `{{alias}}`', ast );
		}
	}
	return {
		'function': hasSignature
	};
}
Rule for enforcing that documentation starts with an alias signature.

@param {Context} context - lint context
@returns {Object} validators