Hidden Appian features

Is there any documentation on some of the hidden features from Appian? For example the library "type!{urn:appian:ps:pdftools}PdfContent". Being able to create files through your expression seems like a very useful feature. However I can't find any formal documentation on this. I know I can do the same on a process model, however it seems simpler this way. 

I also remember seeing somewhere, something along the lines of "type!{namespace}/url/2009/datatype", but like the one above, Appian does not provide information on this.

 

Does anyone have any information about it?

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