[intro.abstract] Actually use the phrase 'unspecified/undefined behavior'

Fixes ISO/CS 011 (C++23 DIS).

Author: jensmaurer

source/intro.tex

@@ -849,7 +849,7 @@
 \pnum
 \indextext{behavior!implementation-defined}%
 Certain aspects and operations of the abstract machine are described in this
-document as implementation-defined (for example,
+document as implementation-defined behavior (for example,
 \tcode{sizeof(int)}). These constitute the parameters of the abstract machine.
 Each implementation shall include documentation describing its characteristics
 and behavior in these respects.
@@ -865,7 +865,7 @@
 \pnum
 \indextext{behavior!unspecified}%
 Certain other aspects and operations of the abstract machine are
-described in this document as unspecified (for example,
+described in this document as unspecified behavior (for example,
 order of evaluation of arguments in a function call\iref{expr.call}).
 Where possible, this
 document defines a set of allowable behaviors. These
@@ -876,7 +876,7 @@
 \pnum
 \indextext{behavior!undefined}%
 Certain other operations are described in this document as
-undefined (for example, the effect of
+undefined behavior (for example, the effect of
 attempting to modify a const object).
 \begin{note}
 This document imposes no requirements on the