Removing value="" from <input> is not always correct

[clarfonthey]

Per the standard, the default value is "on" for radio and checkbox inputs, not empty string:

Minimal example:

<input type="radio" value="">

gets converted to:

<input type=radio>

which is effectively:

<input type=radio value=on>

This should be handled accordingly, based upon the following table:

type	default value
checkbox	on
radio	on
file	C:\fakepath\

For all other types, the default is in fact an empty string. If type is not equal to one of the known types, it should be assumed dynamic and the value thus cannot be removed.