\documentclass{article}
\usepackage{luanumbers}
\LuaNumbersSetup{decimals=1,warnings=error}

\begin{document}
Automatic decimals: 3.14159, 3.00, -1.234, 6.022e2. Integer: 7.

\begin{luanumbersexclude}
\section{Selected object 3.14159}
\label{sec:selected-3.14159}
This selected object remains 3.14159.
\end{luanumbersexclude}

Automatic processing resumes here: 3.14159.

\LuaNumbersOff
\directlua{
  assert(luanumbers.format("3.14159") == "3.1")
  assert(luanumbers.format("3.00") == "3.0")
  assert(luanumbers.format("-1.234") == "-1.2")
}
\LuaNumbersOn
\end{document}