[IMP] developer: add notes on entity references & fix illegal XML

Using `<` inside XML elements will result in a parsing error,
an entity reference should be used instead: `&lt;`.

closes odoo/documentation#5184

X-original-commit: a7743d513b
Signed-off-by: Levi Siuzdak (sile) <sile@odoo.com>
Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

content/developer/reference/backend/views.rst

@@ -2325,11 +2325,14 @@ Possible children elements of the search view are:
 
           <filter domain="[('state', '=', 'draft')]"/>
           <separator/>
-          <filter domain="[('delay', '<', 15)]"/>
+          <filter domain="[('delay', '&lt;', 15)]"/>
 
        if both filters are selected, will select the records whose ``state``
        is ``draft`` **and** ``delay`` is below 15.
 
+       .. note:: XML does not allow ``<`` to be used within XML elements,
+          an entity reference (``&lt;``) should be used instead.
+
 ``separator``
     can be used to separates groups of filters in simple search views