The package provides the means to extract specific content from a source document and write that to a target document. One could, for instance, use this to extract all exercises from lecture notes and generate an exercises book on the fly.

The package also provides an environment which writes its body entirely to the target file. Another environment will write to the target file, but will also execute the body. This allows to share code (for instance, a preamble) between the source document and the target file.

Finally, the package provides an interface to conditionally extract content. With a single option in the \usepackage command, one can specify exactly which commands (counted from the start of the document) should be extracted and which not. This might be useful for extracting specific slides from a presentation and use them in a new file. The author is Hendri Adriaens.