Obsidian Portal users should be accustomed to writing textile and are likely to create textile based input via applications which take advantage of the API. As application authors we don't and shouldn't need to know which version of which textile parser Obsidian Portal is currently using or what the filtering rules applied to inline html currently are. However it would be nice to allow our application's users to preview content they are about to submit.
Therefore I would like to see an API call which accepts text input and returns whatever html results from parsing the input as textile and applying whatever restrictions on inline HTML Obsidian Portal currently thinks are necessary. I think it would make sense for that response to be a full html page and include at least a reasonable set of stylesheets for the default look and feel of html elements on the Obsidian Portal website. However even a context free snippet of html might be helpful in allowing applications to preview the structure of the content a user is attempting to post.