Extra page when using tikzpicture called by AtBeginShipout?

Question

I have been attempting to use \AtBeginShipout and tikz to draw header and footer art as suggested in solution for creating newsletter art by user Gonzalo Medina.

One problem that has been encounter is that an extra page containing only the artwork is always produced at the end of the document. In the example below I expect two pages of output, but there are three. Why is this? What is the best way to prevent it?

Example using \AtBeginShipout with \tikzpicture produces an extra page:

\documentclass{article}

\usepackage{tikz}
\usepackage{atbegshi}
\usepackage{lipsum}

\newcommand\DrawSquare{
\begin{tikzpicture}[overlay]
\draw[fill=pink]
    (0,0) rectangle (10,-10);
\end{tikzpicture}
}

\AtBeginShipout{\DrawSquare}

\begin{document}
\lipsum[1-9]
\end{document}

Thumbnail of Output:

Answer 1

When you use

\AtBeginShipout{<stuff>}

<stuff> is inserted into the input stream. However, at that point, the entire "current page" has already been constructed and is contained inside the box \AtBeginShipoutBox. If you leave everything as-is, the "current page" is shipped out, after which <stuff> is processed.

In your instance, an overlay box is added to the input stream but doesn't form part of the "current page" to be shipped out.

In order to add to the "current page" that will be shipped out, you need to use the combination

\AtBeginShipout{\AtBeginShipoutAddToBox{<stuff>}}

or

\AtBeginShipout{\AtBeginShipoutUpperLeft{<stuff>}}

Answer 2

Replacing:

\AtBeginShipout{\DrawSquare}

With:

\AtBeginShipout{\AtBeginShipoutAddToBox{\DrawSquare}}

Solves the problem. The output consists of two pages of text, both pages contain a pink square. However, I can't explain why the problem occurs or why this solution works.

This solution was found here.