Avoid Text Input
The RSS specification actively discourages publishers from using the textInput element, calling its purpose "something of a mystery" and stating that "most aggregators ignore it." Fewer than one percent of surveyed RSS feeds included the element. The only aggregators known to support it are BottomFeeder and Liferea.
For this reason, publishers should not expect it to be supported in most aggregators.
While this element is not actively harmful, it is generally best to remove it unless you have a specific need for this function.
Not clear? Disagree?
You might be able to find help in one of these fine resources.