Template:ReturnInput/doc

This template simply and quite literally returns its first parameter.

Why this is needed
This template might seem useless, but it is not! Read the following before TfDing it! It is required, sometimes to "encode" markup or text within a template call, as the calling brackets single out that piece of markup in the parser, stopping it from interfering with any templates that the input might be nested in.

Example
A simple example of usage is demonstrated here. A template might have the code:

During usage of this template, if the  parameter is called as " " then it will parse into the template like this (truncated):

This causes the template to think that the final parameter of the  is not a default parameter, but is in fact the key " " as it now reads:

Rewriting the switch as:

allows you to explicitly specify that the equals sign in the URL is not to be taken as a parameter, fixing the problem.

This is just one example of how nesting markup within a template call avoids problematic parsing.