Microsoft Compiled HTML Help

Microsoft Compiled HTML Help

Filename extension	.chm
Internet media type	application/x-chm
Developed by	Microsoft
Initial release	1997
Extended to	.lit
Standard(s)	No

Microsoft Compiled HTML Help A component of Microsoft Windows
Details
Type	Help system
Included with	Windows 98
Replaces	Microsoft WinHelp
Replaced by	Microsoft Help 2

Microsoft Compiled HTML Help is a Microsoft proprietary online help format. It was introduced as the successor to Microsoft WinHelp with the release of Windows 98, and is still supported in Windows 7.

History

In 2002, Microsoft announced security risks associated with the .CHM format, as well as security bulletins and patches.^[1] They have since announced their intentions not to develop the .CHM format further.^[2]

Month	Year	Description
February	1996	Microsoft announces plans to stop development of WinHelp and start development on HTML Help.
August	1997	HTML Help 1.0 (HH 1.0) is released with Internet Explorer 4.
February	1998	HTML Help 1.1a ships with Windows 98.
January	2000	HTML Help 1.3 ships with Windows 2000.
July		HTML Help 1.32 releases with Internet Explorer 5.5 and Windows Me.
October	2001	HTML Help 1.33 releases with Internet Explorer 6 and Windows XP.
March		At the WritersUA (formerly WinWriters) conference, Microsoft announces plans for a new help platform, Help 2, which is also HTML based.
January	2003	Microsoft decides not to release Microsoft Help 2 as a general Help platform.

File format

Help is delivered as a binary file with the .chm. It contains a set of HTML files, a hyperlinked table of contents, and an index file.

The file starts with bytes "ITSF" (in ASCII), for "Info-Tech Storage Format". The format has been reverse-engineered by Matthew Russotto with assistance from Peter Ferrie and Paul Wise.^[3] Russotto's documentation is freely available at http://www.russotto.net/chm/chmformat.html.

On Windows computers a .chm can be built with the freely-distributed HTML Help Workshop.

The published help features:

• Data compression (with LZX compression)
• Built in search engine
• Ability to merge a number of .chm help system
• Extended character support although it does not fully support Unicode.^[4]

The .chm file format's ability to contain and execute arbitrary code is a potential security threat, and viewing .chm files is sometimes restricted in the Windows OS.

Applications

The Microsoft Reader .LIT file format is a modification of the HTML Help CHM format. CHM files are sometimes used for e-books.^[5]

Beyond CHM, a multi-tab CHM reader and CHM editor, which enables user to add annotations on CHM eBooks.

Various applications, such as HTML Help Workshop or 7-Zip, have features to decompile CHM files. On Windows systems, the hh.exe utility, as well as the extract_chmLib utility (a component of chmlib) on Linux systems, can be used to decompile CHM files as well.

Use on non-Windows platforms

• GTK: GnoCHM at SourceForge.net, CHMsee, chmviewkit
• Qt: Okular, kchmviewer, KCHM at SourceForge.net
• Java: CHMPane at SourceForge.net
• iOS: ReadCHM, CHMate
• Mac OS X: CHMox, ArCHMock
• Other / multiple: xCHM, arCHMage at SourceForge.net, DisplayCHM^[6], ChmFox Firefox addon CHM Reader Firefox addon, Free Pascal, FBReader, iChm

See also

• Windows Help
• Microsoft Help 2
• KDE WAR (file format)
• Comparison of documentation generators

References

1. ^ WinWriters - Security and Microsoft Help
2. ^ Microsoft HTML Help Workshop download page
3. ^ HTML Help Maker on Paul Wise (Pabs)' website
4. ^ INFO: Limited Unicode Support in HTML Help
5. ^ Title Handbook of Data Compression Authors David Salomon, Giovanni Motta, David (CON) Bryant Edition 5, illustrated Publisher Springer, 2009 ISBN 1848829027, 9781848829022 Length 1359 pages
6. ^ Displaychm, KDE Service Menu

External links

• HTML Help Web Page on MSDN
• Microsoft Help 2 Reference (part of Visual Studio SDK for VS7.1 and VS8.0)
• History of HTML Help
• Unofficial (Preliminary) HTML Help Specification