The alt-p command displays the source print for the online digital score in the VHV editor.

For most of the online VHV repertories, pressing alt-p will load a PDF of the source edition used to create the digital score. The PDF scan of the source edition is opened in a separate window and can be used proof-reading of the digital score.

For example, going to this link:

displays the following digital score:

digital score.
Digital score and rendered notation.

When pressing alt-p on the above page, the following window will be opened with a PDF file of the source edition:

PDF scan of source score.
PDF of scanned version of source edition.

The VHV editor and source print windows can be resized and arranged for proof-reading:

digital score and print source.
Digital score window about print source window.