[tex-eplain] Undefined label

[Oleg Katsitadze]

On Tue, Apr 28, 2009 at 06:49:26PM +0100, Rodolfo Medina wrote:
> Inside a certain definition, I want to create a condition on the existence of
> an undefined label:

Taken from \@definelabel in xeplain.tex:

    \expandafter\ifx\csname\xrlabel{#1}\endcsname \relax
      % Label is undefined.
    \else
      % Label is defined.
    \fi

Oleg