When determining the generated value attribute the tag looks for a number of attributes. Any supplied value attribute will be ignored if either expr (5.2.2.3) or valueexpr (5.2.2.12) attributes (depending upon input type) present.
If no expr, valueexpr, or value attribute
is present then the value identified by the generated name
(5.2.2.5) attribute will be taken from the local
namespace. If this value is None
then no value
attribute will be written. The name used to look into the local
namespace is the result of evaluating all name related
attributes.
For input field types radio and checkbox the valueexpr attribute if present takes priority over and specified value attribute.
Refer to the documentation for individual input types for more details.