code: function mergeable(node) {
    var start
    var end
  
    if (node.type !== 'text' || !node.position) {
      return true
    }
  
    start = node.position.start
    end = node.position.end
  
    // Only merge nodes which occupy the same size as their `value`.
    return (
      start.line !== end.line || end.column - start.column === node.value.length
    )
  }
docs: Check whether a node is mergeable with adjacent nodes.