The TIDY License:

  Copyright (c) 1998-2015 World Wide Web Consortium
  (Massachusetts Institute of Technology, European Research
  Consortium for Informatics and Mathematics, Keio University).
  All Rights Reserved.

  Contributing Author(s):

     Dave Raggett <[email protected]>

  The contributing author(s) would like to thank all those who
  helped with testing, bug fixes and suggestions for improvements.
  This wouldn't have been possible without your help.

  COPYRIGHT NOTICE:

  This software and documentation is provided "as is," and
  the copyright holders and contributing author(s) make no
  representations or warranties, express or implied, including
  but not limited to, warranties of merchantability or fitness
  for any particular purpose or that the use of the software or
  documentation will not infringe any third party patents,
  copyrights, trademarks or other rights.

  The copyright holders and contributing author(s) will not be held
  liable for any direct, indirect, special or consequential damages
  arising out of any use of the software or documentation, even if
  advised of the possibility of such damage.

  Permission is hereby granted to use, copy, modify, and distribute
  this source code, or portions hereof, documentation and executables,
  for any purpose, without fee, subject to the following restrictions:

  1. The origin of this source code must not be misrepresented.
  2. Altered versions must be plainly marked as such and must
     not be misrepresented as being the original source.
  3. This Copyright notice may not be removed or altered from any
     source or altered source distribution.

  The copyright holders and contributing author(s) specifically
  permit, without fee, and encourage the use of this source code
  as a component for supporting the Hypertext Markup Language in
  commercial products. If you use this source code in a product,
  acknowledgment is not required but would be appreciated.


ADDITIONAL README AND COPYRIGHT NOTICES PRESENT IN SOURCE
CODE FILES:

/* tidylib.c -- internal library definitions

  (c) 1998-2008 (W3C) MIT, ERCIM, Keio University
  See tidy.h for the copyright notice.

  Defines HTML Tidy API implemented by tidy library.

  Very rough initial cut for discussion purposes.

  Public interface is const-correct and doesn't explicitly depend
  on any globals.  Thus, thread-safety may be introduced w/out
  changing the interface.

  Looking ahead to a C++ wrapper, C functions always pass
  this-equivalent as 1st arg.

  Created 2001-05-20 by Charles Reitzel

*/


This copyright header is present in all TIDY source code files. It always
references the file tidy.h as the location of the COPYRIGHT and LICENSE
information.
The copyright start and end years vary from file to file.