Syntax: !jw [-l]
Without arguments, this command will take the most recently selected wire, and recursively join it with other similar (same width and layer) wires that share an end point.
If the -l option is given, all wires on the current layer in the current cell will be joined with any similar wires that share an endpoint.
The command works in electrical and physical modes. Its initial purpose was to fix designs imported from another EDA tool that had all wires as two-vertex segments. Within Xic, an attempt is made to keep wires maximally joined in general, which is more efficient, so this command is probably rarely needed.