<output mediatype=""/>

Here is what we say already about <output/> for different media. It already 
mentions HTML explicitly, and could cover SVG without change.

The mediatype is obtained from the mediatype attribute if present, or 
otherwise from the mediatype child element if any.

If a mediatype has been specified, and the data to be output is non-empty, 
the data is decoded or dereferenced depending on the base type of the data: 
an xs:base64Binary value is base-64 decoded, an xs:hexBinary value is 
hex-binary decoded, and an xs:anyURI value is treated as a URI and 
dereferenced. For any other type, the data is used without modification. 
Implementations should 
<https://www.w3.org/community/xformsusers/wiki/XForms_2.0#intro-conventions>
  accept at least image/* and, if the host language is some version of 
HTML, text/html as possible values of mediatype.

The data is rendered in a suitable way taking into account the datatype of 
the value, the mediatype if any, the appearance attribute, and localization 
and internationalization issues such as representation of numbers and 
dates.

Steven