在使用背景和 TikZ 时，如何避免有关可能更改的标签的持续警告？

Question

上个月，我发布了以下代码作为问题的答案。代码给出了正确的输出。然而，我没有注意到的是特蕾莎做到了它会生成有关未定义标签的警告，无论编译多少次，该警告仍然存在。

LaTeX Warning: Label(s) may have changed. Rerun to get cross-references right.

为什么警告持续存在？我应该怎么做才能避免它？

\documentclass[a4paper]{article}
\usepackage{geometry,tikz}
\usetikzlibrary{calc}
\usepackage[placement=bottom,scale=1,opacity=1]{background}
\backgroundsetup{contents={%
    \begin{tikzpicture}
      \fill [red] (current page.north west) rectangle ($(current page.north east)!.2!(current page.south east)$) coordinate (a);
      \fill [yellow] (current page.south west) rectangle (a);
    \end{tikzpicture}}}
\usepackage{kantlipsum}
\begin{document}
\kant[1-5]
\end{document}

Answer 1

如果我猜的话，那可能是 tikzcurrent page在添加矩形时会考虑变化。添加该overlay选项可避免出现警告。

\documentclass[a4paper]{article}
\usepackage{geometry,tikz}
\usetikzlibrary{calc}
\usepackage[placement=bottom,scale=1,opacity=1]{background}
\backgroundsetup{contents={%
    \begin{tikzpicture}[overlay]
      \fill [red] (current page.north west) rectangle ($(current page.north east)!.2!(current page.south east)$) coordinate (a);
      \fill [yellow] (current page.south west) rectangle (a);
    \end{tikzpicture}}}
\usepackage{kantlipsum}
\begin{document}
\kant[1-5]
\end{document}