What documentation exists for R?

Chapter 7: R Miscellanea 83
title(bquote(hat(a) = .(ahat)))
where subexpressions enclosed in ‘.()’ are replaced by their values.
There are more worked examples in the mailing list achives.
7.14 What are valid names?
When creating data frames using data.frame() or read.table(), R by default ensures
that the variable names are syntactically valid. (The argument ‘check.names’ to these
functions controls whether variable names are checked and adjusted by make.names() if
needed.)
To understand what names are “valid”, one needs to take into account that the term
“name” is used in several different (but related) ways in the language:
1. A syntactic name is a string the parser interprets as this type of expression. It consists
of letters, numbers, and the dot and (for version of R at least 1.9.0) underscore
characters, and starts with either a letter or a dot not followed by a number. Reserved
words are not syntactic names.
2. An object name is a string associated with an object that is assigned in an expression
either by having the object name on the left of an assignment operation or as an
argument to the assign() function. It is usually a syntactic name as well, but can be
any non-empty string if it is quoted (and it is always quoted in the call to assign()).
3. An argument name is what appears to the left of the equals sign when supplying an
argument in a function call (for example, f(trim=.5)). Argument names are also
usually syntactic names, but again can be anything if they are quoted.
4. An element name is a string that identifies a piece of an object (a component of a list,
for example.) When it is used on the right of the ‘$’ operator, it must be a syntactic
name, or quoted. Otherwise, element names can be any strings. (When an object is
used as a database, as in a call to eval() or attach(), the element names become
object names.)
5. Finally, a file name is a string identifying a file in the operating system for reading,
writing, etc. It really has nothing much to do with names in the language, but it is
traditional to call these strings file “names”.
7.15 Are GAMs implemented in R?
Package gam from CRAN implements all the Generalized Additive Models (GAM) functionality
as described in the GAM chapter of the White Book. In particular, it implements
backfitting with both local regression and smoothing splines, and is extendable. There is a
gam() function for GAMs in package mgcv, but it is not an exact clone of what is described
in the White Book (no lo() for example). Package gss can fit spline-based GAMs too. And
if you can accept regression splines you can use glm(). For gaussian GAMs you can use
bruto() from package mda.
7.16 Why is the output not printed when I source() a file?
Most R commands do not generate any output. The command
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