Certain components (most HTML components), by nature, reserve some parameter names to fulfill their contract. Such parameters are called reserved parameters and are specified in the component specification.

For example, the TextField component, by contract, is required to render an HTML text <input> tag. And that requires that the type attribute of the <input> tag be "text". Hence the TextField component reserves the name type for itself. Any TextField declaration that specifies a type parameter is simply ignored.

...
<input jwcid="@TextField" type="text" hidden="ognl:true" ... />
...

Here, although the component declaration specifies the type to be text, the component, when rendered, will be of type hidden.