Has \textsubscript become a standard LaTeX command?

Question

TeX Live comes with a helpful fragment package, subscript, the copyright notice of which runs as follows:

% Copyright 1999 Robin Fairbairns
%
% this fragment is distributed under the conditions of the LaTeX
% Project Public Licence -- see lppl.txt in the LaTeX distribution
%
% this fragment provides a command \textsubscript, which is
% shamelessly copied from the command \textsuperscript that's part of
% LaTeX
%
% the fragment may be used as a package in its own right, if so
% needed.

I may be wrong but LaTeX used not to have a \textsubscript analogous to standard \textsuperscript. But now the following document compiles under pdftex from TeX Live 2016:

\documentclass{article}
\begin{document}
x\textsubscript{1}
\end{document}

However, upon compilation, the log file doesn't mention the subscript package. Nor does pdftex complain if \usepackage{subscript}, but, strangely enough, it does complain if \newcommand\textsubscript[1]{}. What is going on here? Has \textsubscript become a standard LaTeX command? Can I just stop requesting subscript from now on?

IIRC \textsubscript has been added (along with other stuff previously covered by the fixltx2e package) to the kernel in the 2015/01/01 release. — cgnieder, Dec 18 '16 at 12:53
The \textsubscript command had been added to fixltx2e in 2005. — egreg, Dec 18 '16 at 13:29

score 12 · Accepted Answer · answered Dec 18 '16 at 13:27

The \textsubscript command was for many years part of fixltx2e: code which the team felt should be in the kernel but for various reasons did not want to add. At the start of 2015, there was a policy change and the contents of fixltx2e were 'folded' into the kernel. (There is a mechanism to back this out if required.) As a result, any recent LaTeX provides \textsubscript.

Has \textsubscript become a standard LaTeX command?

1 Answers1