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<h3 class="section">3.20 tkerror</h3>
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<p>tkerror \- Command invoked to process background errors
<h4 class="unnumberedsubsec">Synopsis</h4>
<p><b>tkerror </b><i>message</i>
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<h4 class="unnumberedsubsec">Description</h4>
<p>The <b>tkerror</b> command doesn't exist as built-in part of Tk. Instead,
individual applications or users can define a <b>tkerror</b>
command (e.g. as a Tcl procedure) if they wish to handle background
errors.
<p>A background error is one that occurs in a command that didn't
originate with the application. For example, if an error occurs
while executing a command specified with a <b>bind</b><span class="roman"> of </span><b>after</b>
command, then it is a background error. For a non-background error,
the error can simply be returned up through nested Tcl command
evaluations until it reaches the top-level code in the application;
then the application can report the error in whatever way it
wishes. When a background error occurs, the unwinding ends in
the Tk library and there is no obvious way for Tk to report
the error.
<p>When Tk detects a background error, it invokes the <b>tkerror</b>
command, passing it the error message as its only argument.
Tk assumes that the application has implemented the <b>tkerror</b>
command, and that the command will report the error in a way that
makes sense for the application. Tk will ignore any result returned
by the <b>tkerror</b> command.
<p>If another Tcl error occurs within the <b>tkerror</b> command
then Tk reports the error itself by writing a message
to stderr.
<p>The Tk script library includes a default <b>tkerror</b> procedure
that posts a dialog box containing the error message and offers
the user a chance to see a stack trace that shows where the
error occurred.
<h4 class="unnumberedsubsec">Keywords</h4>
<p>background error, reporting
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