Clarify initial-frame-alist and default-frame-alist.

lispref/frames.texi

@@ -194,7 +194,9 @@ by setting @code{initial-frame-alist} in your @file{.emacs} file.
 
 @defvar initial-frame-alist
 This variable's value is an alist of parameter values used when creating
-the initial X window frame.  Each element has the form:
+the initial X window frame.  You can set this variable to specify the
+appearance of the initial frame without altering subsequent frames.
+Each element has the form:
 
 @example
 (@var{parameter} . @var{value})
@@ -231,8 +233,9 @@ to the parameters for the main initial frame.
 @end defvar
 
 @defvar default-frame-alist
-This is an alist specifying default values of frame parameters for
-subsequent Emacs frames (not the initial ones).
+This is an alist specifying default values of frame parameters for all
+Emacs frames---the first frame, and subsequent frames.  In many cases,
+you can get the same results by means of X resources.
 @end defvar
 
 See also @code{special-display-frame-alist}, in @ref{Choosing Window}.