[Tex/LaTex] How come Revtex says acknowledgements are obsolete

obsoleterevtexwarnings

Running revtex4-1 with the preamble:

\documentclass[aps, pre, floatfix, reprint]{revtex4-1}

and the section later:

\begin{acknowledgements}
The authors would like to thank Tex, LaTeX and Friends 
for the answer to this question.
\end{acknowledgements}

Gives the warning:

 Class revtex4-1 Warning: Environment acknowledgements is obsolete;

Have I done something wrong here?

Best Answer

I have never used revtex but the author's guide explicitly states:

Please note the spelling of “acknowledgments.”

This is also the full error message LaTeX produces:

Class revtex4-1 Warning: Environment acknowledgements is obsolete; Use acknowledgments instead.

So replacing acknowledgements by acknowledgments removes the message.

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