What's the deal with Tex Live and expl3.sty?

Question

I've installed Tex Live 2010 on a mac, and when trying to use xelatex, I get the error:

!Latex Error: File `expl3.sty' not found

What is this package, and how can I get it installed on tex live? There are no updates available, according to the Tex Live utility.

Update: I've found the 'tlmgr' utility, and done: sudo tlmgr install expl3

So far, so good. Unfortunately, I am now told I need xparse.sty. xparse.sty is not available through tlmgr ("package xparse not present in package repository").

Needless to say, I am not using xparse directly, nor am I directly using calc.sty, which is the file that was mentioned just before this error.

Further update: xparse is obtained by installing 'xpackages'.

Answer 1

It's a wrapper package used by various packages which rely on some experimental pieces of the LaTeX3 project. See here

To install it, open a terminal and type:

sudo tlmgr install expl3

Oops, now seen your edit. Try:

sudo tlmgr install xpackages

It might be necessary to do an update your system:

sudo tlmgr update -self -all

Answer 2

When the name of the TeX Live package containing a given file isn't obvious, you can ask tlmgr about it:

$ tlmgr search --global --file xparse.sty
tlmgr: package repository /home/mpg/tl/trunk/Master
xpackages:
    texmf-dist/tex/latex/xpackages/xbase/xparse.sty

Then use tlmgr install to install the required package.