The Read-Only attribute
This bit is useful to make a file write-protected by
software. Read only files will not be deleted under normal
circumstances. Certain files in Windows are kept as
Read-only by default (e.g., the system registry files).
Before you can delete or overwrite a Read-only file, you must
remove the Read-only file attribute bit.
The Hidden and System attribute
The purpose of the Hidden attribute bit is to make the
file invisible in certain applications file list display.
Since many file applications have the feature to ignore the
Hidden attribute bit, files with the Hidden attribute bit are
not always invisible.
The System attribute specifies that the file is part of the operating system or is used exclusively by the operating system.
The Archive attribute
The purpose of the Archive attribute is to quickly
determine whether a file requires a back up (archiving). The
Archive attribute is set whenever an existing file is either
overwritten or modified (i.e., renamed or moved to another
directory) by the file system.
A new file is usually created with the Archive attribute set. The idea is to have a utility or application program to take the responsibility of clearing the Archive bit when a file is successfully backed up. The next system backup operation will be made much more efficient by focusing only on the files with the Archive attribute bit set which are either newly created or modified in any way since all the Archive attributes are cleared the last time (i.e., the last backup time).
HTML Tidy is a program whose purpose is to fix invalid
HTML and give the source code a reasonable layout (aka indent
Examples of bad code it is able to fix: