lepton-schematic will accept any string as a value for the refdes.
However, some back-ends to lepton-netlist impose restrictions on the
allowed syntax.
Specifically, lepton-sch2pcb requires:
_” is OK.
NAND gates on the schematic called U1a,
U1b, U1c, and U1d. They will netlist into a
single footprint named U1.