Template:FormattingError/doc

Outputs an error message in red into the page and adds the page to Category:Pages with incorrect formatting templates use. An anchor (FormattingError) is inserted at the start of the error message, so you can find any errors on a page easily by adding #FormattingError at the end of the URL (e.g. Template:val/test). Used in complex templates that check their arguments for validity, so incorrect use can be spotted while editing a page or afterwards.

Usage
or

When using the nocategory argument, the error message is displayed as usual, but the page is not added to Category:Pages with incorrect formatting templates use. This is useful in documentation pages for templates that use FormattingError and show what errors they can generate without adding these documentation pages to the category. For an example of this, see LinkForElement.

This template can be evaluated using the  parser function: