XmTextInsert() to add the dashes when appropriate. The problem with this approach is that XmTextInsert()
activates the XmNmodifyVerifyCallback function again, so the dash would be subject to the input filtering.
As a result, the only way to handle the situation is to actually add the dashes in the
XmN-modifyVerifyCallback routine at the same time the digits are added. This approach involves modifying
the ptr and length fields of the XmTextBlock structure in the XmTextVerifyCallbackStruct. The
check_phone() routine checks the current length of the phone number. If it is either two or six characters long, the
routine reallocates ptr to hold two characters, adds the dash, and increments length to account for the dash.
When the Text widget adds the digit and the dash, it positions the insertion cursor at the end of the new text. Prior to
Motif 1.2, the position of the insertion cursor was not affected by the amount of text that was added. The workaround
to this problem was to use the XmNvalueChangedCallback and call XmTextSetInsertionPosition().
Although we haven't demonstrated its use, the XmNvalueChangedCallback is useful when you need to keep
track of the changes in a Text widget, but you don't need to monitor or change the input before it is displayed. This
callback is invoked after the text has been modified in any way, which means that it is called for each insertion and
deletion. The call_data parameter to the routine is of type XmAnyCallbackStruct; the reason field is
always XmCR_VALUE_CHANGED ...