Build an input rule for automatically wrapping a textblock when a given string is typed. When using a regular expresion you’ll probably want the regexp to start with ^, so that the pattern can only occur at the start of a textblock.

type is the type of node to wrap in.

By default, if there’s a node with the same type above the newly wrapped node, the rule will try to join those two nodes. You can pass a join predicate, which takes a regular expression match and the node before the wrapped node, and can return a boolean to indicate whether a join should happen.