Having a custom post type "Articles" with custom taxonomies "volume, issue, authors, Keywords ... etc". I need to add a button on the single post type front-end to let visitors download an xml file of the article that they read. This means an xml file about only the article being read. an example of such issue can be found on this link: https://stephenpalmer.wordpress.com/article/article-the-practice-model-of-coaching-towards-a-solution-focused-approach/ it's generated using the Annotum wordpress theme, & it includes specific data from the specific article. My question is: How can I make my theme do the same? I've tried several xml plugins but they didn't provide me with a solution of this issue. Any suggestions please?
Typically when you want to create an extra representation or variation it implies extending URL a bit and treating that case differently.
The easiest way in WP for that are rewrite endpoints.
However the ease is relative you still need to handle with code the changes in a query and how to produce output. WP doesn't have an easy native concept of multiple representations of content so there aren't really turn-key solutions for that.