ParsoidDocument is a library which implements a Parsoid-compatible document handler using an HTML5 IFrame. It is not a userscript, but is instead loaded by other userscripts. The IFrame contains the Parsoid document, which can then be modified using standard DOM functions. This is used to perform Parsoid-dependent operations in the browser without having to pull in the entirety of the VisualEditor codebase.
Since this library is currently not a gadget, it cannot be minified and optimized by ResourceLoader, making a script's loading process a bit slower. No need to fear: a decently-long cache time should be enough to mitigate the load time issues presented by using this library.
Discussion edit
Forward any discussion and/or report all bugs to my talk page.