# HG changeset patch
# User Adam Chlipala <adam@chlipala.net>
# Date 1292115442 18000
# Node ID dab85a49e0abdc7628bcadac53c117fa5fef3d47
# Parent  4dd5d23bace274085abaa72a7e4e6f24325349cd
Warn about XHTML looseness

diff -r 4dd5d23bace2 -r dab85a49e0ab doc/manual.tex
--- a/doc/manual.tex	Sat Dec 11 15:16:04 2010 -0500
+++ b/doc/manual.tex	Sat Dec 11 19:57:22 2010 -0500
@@ -1819,7 +1819,7 @@
 
 \subsection{XML}
 
-Ur/Web's library contains an encoding of XML syntax and semantic constraints.  We make no effort to follow the standards governing XML schemas.  Rather, XML fragments are viewed more as values of ML datatypes, and we only track which tags are allowed inside which other tags.
+Ur/Web's library contains an encoding of XML syntax and semantic constraints.  We make no effort to follow the standards governing XML schemas.  Rather, XML fragments are viewed more as values of ML datatypes, and we only track which tags are allowed inside which other tags.  The Ur/Web standard library encodes a very loose version of XHTML, where it is very easy to produce documents which are invalid XHTML, but which still display properly in all major browsers.  The main purposes of the invariants that are enforced are first, to provide some documentation about the places where it would make sense to insert XML fragments; and second, to rule out code injection attacks and other abstraction violations related to HTML syntax.
 
 The basic XML type family has arguments respectively indicating the \emph{context} of a fragment, the fields that the fragment expects to be bound on entry (and their types), and the fields that the fragment will bind (and their types).  Contexts are a record-based ``poor man's subtyping'' encoding, with each possible set of valid tags corresponding to a different context record.  The arguments dealing with field binding are only relevant to HTML forms.
 $$\begin{array}{l}