diff --git a/gen/ui/template.pt b/gen/ui/template.pt
index 9a08dd6..9f49b27 100644
--- a/gen/ui/template.pt
+++ b/gen/ui/template.pt
@@ -1,4 +1,4 @@
-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
+<!DOCTYPE html>
 <html metal:define-macro="main"
       tal:define="user tool/getUser;
                   isAnon tool/userIsAnon;
diff --git a/pod/actions.py b/pod/actions.py
index 3654410..2243e20 100644
--- a/pod/actions.py
+++ b/pod/actions.py
@@ -69,7 +69,12 @@ class BufferAction:
             if self.buffer.caller() == 'px':
                 # Add in the error message the line nb where the errors occurs
                 # within the PX.
-                import pdb; pdb.set_trace()
+                locator = self.buffer.env.parser.locator
+                # The column number may not be given.
+                col = locator.getColumnNumber()
+                if col == None: col = ''
+                else: col = ', column %d' % col
+                errorMessage += ' (line %s%s)' % (locator.getLineNumber(), col)
             raise Exception(errorMessage)
         # Empty the buffer
         self.buffer.__init__(self.buffer.env, self.buffer.parent)
@@ -274,7 +279,7 @@ class VariablesAction(BufferAction):
         # every defined variable.
         BufferAction.__init__(self, name, buffer, None, elem, minus, source,
                               fromExpr)
-        # Definitions of variables: ~{s_name: s_expr}~
+        # Definitions of variables: ~[(s_name, s_expr)]~
         self.variables = variables
 
     def do(self):
@@ -286,7 +291,7 @@ class VariablesAction(BufferAction):
         # hide in the context: after execution of this buffer we will restore
         # those values.
         hidden = None
-        for name, expr in self.variables.iteritems():
+        for name, expr in self.variables:
             # Evaluate the expression
             result, error = self.evaluateExpression(expr)
             if error: return
@@ -303,7 +308,7 @@ class VariablesAction(BufferAction):
         # Restore hidden variables if any
         if hidden: context.update(hidden)
         # Delete not-hidden variables
-        for name in self.variables.iterkeys():
+        for name, expr in self.variables:
             if hidden and (name in hidden): continue
             del context[name]
 # ------------------------------------------------------------------------------
diff --git a/pod/buffers.py b/pod/buffers.py
index 92a7e8d..31fcfd0 100644
--- a/pod/buffers.py
+++ b/pod/buffers.py
@@ -140,7 +140,7 @@ class Buffer:
     def getLength(self): pass # To be overridden
 
     def dumpStartElement(self, elem, attrs={}, ignoreAttrs=(),
-                         insertAttributesHook=False):
+                         insertAttributesHook=False, noEndTag=False):
         '''Inserts into this buffer the start tag p_elem, with its p_attrs,
            excepted those listed in p_ignoreAttrs. If p_insertAttributesHook
            is True (works only for MemoryBuffers), we will insert an Attributes
@@ -162,7 +162,12 @@ class Buffer:
             res = self.addAttributes()
         else:
             res = None
-        self.write('>')
+        # Close the tag
+        if noEndTag:
+            suffix = '/>'
+        else:
+            suffix = '>'
+        self.write(suffix)
         return res
 
     def dumpEndElement(self, elem):
@@ -201,7 +206,9 @@ class FileBuffer(Buffer):
     def addExpression(self, expression, tiedHook=None):
         # At 2013-02-06, this method was not called within the whole test suite.
         try:
-            self.dumpContent(Expression(expression).evaluate(self.env.context))
+            res, escape = Expression(expression).evaluate(self.env.context)
+            if escape: self.dumpContent(res)
+            else: self.write(res)
         except Exception, e:
             PodError.dump(self, EVAL_EXPR_ERROR % (expression, e), dumpTb=False)
 
@@ -360,15 +367,15 @@ class MemoryBuffer(Buffer):
         return attrs
 
     def _getVariables(self, expr):
-        '''Returns variable definitions in p_expr as a dict
-           ~{s_varName: s_expr}~.'''
+        '''Returns variable definitions in p_expr as a list
+           ~[(s_varName, s_expr)]~.'''
         exprs = expr.strip().split(';')
-        res = {}
+        res = []
         for sub in exprs:
             varRes = MemoryBuffer.varRex.match(sub)
             if not varRes:
                 raise ParsingError(BAD_VAR_EXPRESSION % sub)
-            res[varRes.group(1)] = varRes.group(2)
+            res.append(varRes.groups())
         return res
 
     def createAction(self, statementGroup):
@@ -624,7 +631,9 @@ class MemoryBuffer(Buffer):
                 currentIndex = index + 1
                 if isinstance(evalEntry, Expression):
                     try:
-                        result.dumpContent(evalEntry.evaluate(self.env.context))
+                        res, escape = evalEntry.evaluate(self.env.context)
+                        if escape: result.dumpContent(res)
+                        else: result.write(res)
                     except Exception, e:
                         if self.caller() == 'pod':
                             PodError.dump(result, EVAL_EXPR_ERROR % (
diff --git a/pod/elements.py b/pod/elements.py
index 75617da..4054f9b 100644
--- a/pod/elements.py
+++ b/pod/elements.py
@@ -89,7 +89,13 @@ class Expression(PodElement):
 
     def evaluate(self, context):
         '''Evaluates the Python expression (self.expr) with a given
-           p_context.'''
+           p_context, and returns the result. More precisely, it returns a
+           tuple (result, escapeXml). Boolean escapeXml indicates if XML chars
+           must be escaped or not. For example, if the expression's result is a
+           PX, the result of evaluating it (a chunk of XHTML) must be inserted
+           as is, unescaped, into the buffer. In most situations, XML escaping
+           will be enabled.'''
+        escapeXml = True
         # Evaluate the expression, or get it from self.result if it has already
         # been computed.
         if self.evaluated:
@@ -103,16 +109,22 @@ class Expression(PodElement):
             # Evaluates the Python expression
             res = self.result = eval(self.expr, context)
         # Converts the expression result to a string that can be inserted into
-        # the POD result.
-        if res == None:
+        # the POD/PX result.
+        resultType = res.__class__.__name__
+        if resultType == 'NoneType':
             res = u''
-        elif isinstance(res, str):
-            res = unicode(res.decode('utf-8'))
-        elif isinstance(res, unicode):
-            pass
+        elif resultType == 'str':
+            res = res.decode('utf-8')
+        elif resultType == 'unicode':
+            pass # Don't perform any conversion, unicode is the target type.
+        elif resultType == 'Px':
+            # A PX that must be called within the current PX. Call it with the
+            # current context.
+            res = res(context)
+            escapeXml = False
         else:
             res = unicode(res)
-        return res
+        return res, escapeXml
 
 class Attributes(PodElement):
     '''Represents a bunch of XML attributes that will be dumped for a given tag
diff --git a/px/px_parser.py b/px/px_parser.py
index 6253c56..1abab74 100644
--- a/px/px_parser.py
+++ b/px/px_parser.py
@@ -54,6 +54,8 @@ class PxEnvironment(XmlEnvironment):
 class PxParser(XmlParser):
     '''PX parser that is specific for parsing PX data.'''
     pxAttributes = ('var', 'for', 'if')
+    # No-end tags
+    noEndTags = ('br', 'img')
 
     def __init__(self, env, caller=None):
         XmlParser.__init__(self, env, caller)
@@ -78,7 +80,7 @@ class PxParser(XmlParser):
             e.currentBuffer.addElement(elem, elemType='px')
         if elem != 'x':
             e.currentBuffer.dumpStartElement(elem, attrs,
-                                             ignoreAttrs=self.pxAttributes)
+                ignoreAttrs=self.pxAttributes, noEndTag=elem in self.noEndTags)
 
     def endElement(self, elem):
         e = self.env
@@ -88,7 +90,8 @@ class PxParser(XmlParser):
             e.currentBuffer.addExpression(e.currentContent)
             e.currentContent = ''
         # Dump the end element into the current buffer
-        if elem != 'x': e.currentBuffer.dumpEndElement(elem)
+        if (elem != 'x') and (elem not in self.noEndTags):
+            e.currentBuffer.dumpEndElement(elem)
         # If this element is the main element of the current buffer, we must
         # pop it and continue to work in the parent buffer.
         if e.isActionElem(elem):
