function visitor( node, index, parent ) {
		if ( EQN_START.test( node.value ) === true ) {
			debug( 'Found an equation...' );
			equations.push({
				'node': node,
				'parent': parent,
				'index': index
			});
		}
	}
Callback invoked upon finding a matching node.

@private
@param {Object} node - AST node
@param {number} index - position of `node` in `parent`
@param {Object} parent - parent AST node
@returns {void}