[Rd] substitute with plots (PR#10987)

[bob.ohara at helsinki.fi]

Full_Name: Bob O'Hara
Version: 2.6.2
OS: Windows
Submission from: (NULL) (128.214.72.197)


Wishlist: This is a documentation problem/complaint/whinge.

The help for substitute() tells us "The typical use of substitute is to create
informative labels for data sets and plots."  But the example given is trivial
and not a lot of use for the sorts of labels we usually require.  FAQ 7.13
explains how to substitute values into plot labels, so it would be useful to put
this as an example in the help page too.

Actually, a few more examples might be useful, so we don't have to guess what
order to put the substitute, paste, and expression (or eval, bquote and paste)!