I've created a HTML based template in a datagrid with this content:
<img src='data:image/png;base64, ${data.Bestand}' />
What I would expect to happen is that only the ${data.Bestand} element is processed during generation, but it isn't. The first data: is also replaced by the template context element.
What I would expect to end up with would be:
<img src='data:image/png;base64, @(-templatecontext-.Bestand)' />
In addition. It seems you are doing a global find and replace for "data". I tried adding an attribute with name 'data', but that one was also replaced by the page's data model '.......Models....DatabaseDossierFoto'. That is not correct of course.