ExtJS: default validation

ExtJS: default validation

95% of my fields for a form I have use a custom validator -> hence I
include it as apart of my defaults config of the container.
However, for the remaining 5% of fields, I want to use the built-in
validation. Is there a way to manually specify using the default validator
for a given field type?
Currently I try,
{
name: 'normalNumberField',
xtype: 'numberfield',
validator: Ext.form.field.Number.validate,
...
}
but I'm getting an error that Ext.form is undefined (why? I clearly have a
reference to Ext ... )