Slightly improve documentation

doc/ref/mloop.xml

@@ -986,24 +986,30 @@ or <C>brk></C> or <C>brk_<A>nn</A>></C> prompt.
 </ManSection>
 
 <ManSection>
-<Func Name="GapExitCode" Arg='ret'/>
+<Func Name="GapExitCode" Arg='[ret]'/>
 
 <Description>
-A <C>GapExitCode</C> sets the return value which will be used when
-&GAP; exits. This may be an integer, or a boolean (where
-<K>true</K> is interpreted as 0, and
-<K>false</K> is interpreted as 1.
-<P/>
+<Ref Func="GapExitCode"/> sets the exit value which is returned
+to the operating system (or parent process) when &GAP; exits.
+This may be an integer in the range [-128..127] (other values
+are reduced modulo 256), or a boolean. <K>true</K> corresponds
+to the return value 0, which by convention is treated as "success".
+<K>false</K> corresponds to the return value 1, which by convention
+is treated as "failure". The exit value is not changed if no argument
+is given.
+<P/>
+The <E>previous</E> exit code is returned.
 </Description>
 </ManSection>
 
 <ManSection>
 <Func Name="QuitGap" Arg='[ret]'/>
 
 <Description>
-A <C>QuitGap</C> acts similarly to the keyword <C>quit</C>. It exits
+<Ref Func="QuitGap"/> acts similarly to the keyword <C>QUIT</C>, except
+<C>QUIT</C> can not be called from a function. It exits
 &GAP; cleanly, calling any function installed using <C>InstallAtExit</C>.
-The optional argument will be passed to <C>GapExitCode</C>.
+The optional argument <A>ret</A> will be passed to <Ref Func="GapExitCode"/>.
 <P/>
 </Description>
 </ManSection>
@@ -1012,10 +1018,11 @@ The optional argument will be passed to <C>GapExitCode</C>.
 <Func Name="ForceQuitGap" Arg='[ret]'/>
 
 <Description>
-A <C>ForceQuitGap</C> is similar to <C>QuitGap</C>, except it ignores any
+<Ref Func="ForceQuitGap"/> is similar to <Ref Func="QuitGap"/>, except it ignores any
 functions installed with <C>InstallAtExit</C>, or any other functions
-normally run at GAP exit, and exits GAP immediately.
-The optional argument will be passed to <C>GapExitCode</C>.
+normally run at GAP exit, such as flushing any partially outputted lines
+to both the screen and files, and exits GAP immediately.
+The optional argument <A>ret</A> will be passed to <Ref Func="GapExitCode"/>.
 <P/>
 </Description>
 </ManSection>
@@ -1434,4 +1441,3 @@ interpret.
 <!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
 <!-- %% -->
 <!-- %E -->
-