update docs

packages/xml/xml.lpa.pl

@@ -26,9 +26,29 @@
 
  * xml is intended to be a rather modular module: it should be easy to
 
+ * build a program that can output XML, but not read it, or vice versa.
+
+ * Similarly, you may be happy to dispense with diagnosis once you are
+
+ * sure that your code will only try to make valid calls to xml_parse/2.
+
+ *
+
+ * It is intended that the code should be very portable too. Clearly,
+
  * some small changes will be needed between platforms, but these should
 
  * be limited to xml_utilities. xml_utilities contains most of the shared
+
+ * code and most of the potentially non-portable code.
+
+ */
+
+:- ensure_loaded( xml_driver ).
+
+
+
+/* atom_codes/2, number_codes/2 and throw/1 are ISO predicates, mapped to
 
  * the Quintus equivalent here.
 
@@ -53,6 +73,14 @@ select( Element, [H|T0], [H|T1] ):-
 /** @pred  number_codes(? _A_,? _L_) is iso 
 
 
+The predicate holds when at least one of the arguments is ground
+(otherwise, an error message will be displayed). The argument  _A_
+will be unified with a number and  _L_ with the list of the ASCII
+codes for the characters of the external representation of  _A_.
+
+ 
+*/
+number_codes( Number, Codes ) :-
 
 	number_chars( Number, Codes ).