If there is an encoding-specific symbol command cmd but there is no
\DeclareTextSymbol for that encoding, then this command
will pick up the slack, by saying to get the symbol as described for
For example, to declare that if the current encoding has no meaning for
\textdollar then use the one from
OT1, declare this.
That is, this command is equivalent to this call (see \UseTextAccent & \UseTextSymbol).
\DeclareTextSymbolDefault can be used to define a
default for any zero-argument fontenc command.