Login 1.9.0 Register snippet and controller do not follow standards
The Register snippet and its controller do not follow the standards for the Login package. The HTML mark-up to be applied to error messages cannot be over-ridden.
In general the Login package snippets use a pair of properties: &errTpl and &errTplType to have the text of messags being put into error place-holders (such as [[+error.username]] wrapped in HTML mark-up. The default for &errTplType is normally modChunk and the default for &errTpl is normally the chunk, "lgnErrTpl".
Register does not have an &errTplType (or if it does, it doesn't work). &errTpl is the actual text to be used by the register controller. In the Register controller, it is given the default value of '[[+error]]' and effectively that cannot be over-ridden. That is because '[[+error]]' cannot be coded in the resource/chunk containing the Register snippet invocation as the tag evaluation process will attempt to evaluate it, rather than pass it unchanged to the controller.