Guide to LaTeX (4th Edition) (Tools and Techniques

432 Appendix C. Error Messages
C.5.2 L AT E X package warnings
The class and package warnings are those that check the names and
versions of the loaded files against those requested, or the use of options,
or whether the filecontents environment has written some text to a
file. The commands involved are described in Section D.2.9.
Classes and packages can also issue their own warnings which are
peculiar to them. These cannot be listed here, since they depend entirely
on the class or package itself.
LaTeX Warning: File ‘...’ already exists on the system.
Not generating it from this source.
The filecontents environment is not extracting text from the main file
because it has discovered a file of the same name already on the system.
LaTeX Warning: Unused global option(s):.
Options specified in the \documentclass statement are global, meaning
they can apply to the class and/or to any following packages. However,
if no class or package recognizes any of these options, this warning is
printed, followed by a list of the unused options.
LaTeX Warning: Writing file ‘...’.
The filecontents environment (Section D.2.9) is extracting text out of
the main file and writing it to a file of the given name.
LaTeX Warning: You have requested class/package ‘...’,
but the class/package provides ‘...’.
The name of the class or package as given by its internal identifying
command \ProvidesClass or \ProvidesPackage does not agree with
the file that was read in with \usepackage or \RequirePackage.
LaTeX Warning: You have requested, on input line ..., version
‘...’ of class/package ...,
but only version ‘...’ is available.
The date of a class or package file, as given by its internal identifying
command \ProvidesClass or \ProvidesPackage, is earlier than that
asked for by the \usepackage or \RequirePackage command. The class
or package may not have all the features that the inputting file expects.
LaTeX Warning: You have requested release ‘...’ of LaTeX,
but only release ‘...’ is available.
The date of your L AT E X version is earlier than that specified for some input
file in a \NeedsTeXFormat command (Section D.2.1). Your L AT E X may not
provide all the features needed by that file.