explained how wxCB_READONLY works (under MSW) better

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_2_BRANCH@7909 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/combobox.tex

@@ -23,8 +23,9 @@ A combobox permits a single selection only. Combobox items are numbered from zer
 \begin{twocollist}\itemsep=0pt
 \twocolitem{\windowstyle{wxCB\_SIMPLE}}{Creates a combobox with a permanently displayed list. Windows only. }
 \twocolitem{\windowstyle{wxCB\_DROPDOWN}}{Creates a combobox with a drop-down list.}
-\twocolitem{\windowstyle{wxCB\_READONLY}}{Creates a combo box consisting of a drop-down list and static text item
-displaying the current selection.}
+\twocolitem{\windowstyle{wxCB\_READONLY}}{Same as wxCB\_DROPDOWN but only the
+strings specified as the combobox choices can be selected, it is impossible to
+select (even from a program) a string which is not in the choices list.}
 \twocolitem{\windowstyle{wxCB\_SORT}}{Sorts the entries in the list alphabetically.}
 \end{twocollist}
 
@@ -319,6 +320,9 @@ wxPython.}
 
 Sets the text for the combobox text field.
 
+{\bf NB:} For a combobox with {\tt wxCB\_READONLY} style the string must be in
+the combobox choices list, otherwise the call to SetValue() is ignored.
+
 \wxheading{Parameters}
 
 \docparam{text}{The text to set.}