The HTML Help 1.0 specification aka CHM files, is pretty old. In fact, it's practically ancient as it was introduced in 1997 when Internet Explorer 4 was introduced. Html Help 1.0 is basically a completely HTML based Help system that uses a Help Viewer that internally uses Internet Explorer to render the HTML Help content. Because of its use of the Internet Explorer shell for rendering there were many security issues in the past, which resulted in locking down of the Web Browser control in Windows and also the Help Engine which caused some unfortunate side effects.
Even so, CHM continues to be a popular help format because it is very easy to produce content for it, using plain HTML and because it works with many Windows application platforms out of the box. While there have been various attempts to replace CHM help files CHM files still seem to be a popular choice for many applications to display their help systems. The biggest alternative these days is no system based help at all, but links to online documentation.
For Windows apps though it's still very common to see CHM help files and there are still a ton of CHM help out there and lots of tools (including our own West Wind Html Help Builder) that produce output for CHM files as well as Web output.
Image is Everything and you ain't got it!
One problem with the CHM engine is that it's stuck with an ancient Internet Explorer version for rendering. For example if you have help content that uses HTML5 or CSS3 content you might have an HTML Help topic like the following shown here in a full Web Browser instance of Internet Explorer:
The page clearly uses some CSS3 features like rounded corners and box shadows that are rendered using plain CSS 3 features. Note that I used Internet Explorer on purpose here to demonstrate that IE9 on Windows 7 can properly render this content using some of the new features of CSS, but the same is true for all other recent versions of the major browsers (FireFox 3.1+, Safari 4.5+, WebKit 9+ etc.).
Unfortunately if you take this nice and simple CSS3 content and run it through the HTML Help compiler to produce a CHM file the resulting output on the same machine looks a bit less flashy:
All the CSS3 styling is gone and although the page display and functionality still works, but all the extra styling features are gone. This even though I am running this on a Windows 7 machine that has IE9 that should be able to render these CSS features. Bummer.
Web Browser Control - perpetually stuck in IE 7 Mode
The problem is the Web Browser/Shell Components in Windows. This component is and has been part of Windows for as long as Internet Explorer has been around, but the Web Browser control hasn't kept up with the latest versions of IE. In a nutshell the control is stuck in IE7 rendering mode for engine compatibility reasons by default. However, there is at least one way to fix this explicitly using Registry keys on a per application basis.
The key point from that blog article is that you can override the IE rendering engine for a particular executable by setting one (or more) registry flags that tell the Windows Shell which version of the Internet Explorer rendering engine to load. An application that wishes to use a more recent version of Internet Explorer can then register itself during installation for the specific IE version desired and from then on the application will use that version of the Web Browser component. If the application is older than the specified version it falls back to the default version (IE 7 rendering).
Forcing CHM files to display with IE9 (or later) Rendering
Knowing that we can force the IE usage for a given process it's also possible to affect the CHM rendering by setting same keys on the executable that's hosting the CHM file. What that executable file is depends on the type of application as there are a number of ways that can launch the help engine.
The standalone Windows CHM Help Viewer that launches when you launch a CHM from Windows Explorer. You can manually add hh.exe to the registry keys.
If you're using .NET or any tool that internally uses the hhControl ActiveX control to launch help content your application is your host. You should add your application's exe to the registry during application startup.
If you're building a FoxPro application that uses the built-in help features, foxhhelp9.exe is used to actually host the help controls. Make sure to add this executable to the registry.
What to set
You can configure the Internet Explorer version used for an application in the registry by specifying the executable file name and a value that specifies the IE version desired.
There are two different sets of keys for 32 bit and 64 bit applications.
32 bit only or 64 bit:
Value Key: hh.exe
32 bit on 64 bit machine:
Value Key: hh.exe
Note that it's best to always set both values ideally when you install your application so it works regardless of which platform you run on.
The value specified is a DWORD value and the interesting values are decimal 9000 for IE9 rendering mode depending on !DOCTYPE settings or 9999 for IE 9 standards mode always. You can use the same logic for 8000 and 8888 for IE8 and the final value of 7000 for IE7 (one has to wonder what they're going todo for version 10 to perpetuate that pattern).
I think 9000 is the value you'd most likely want to use. 9000 means that IE9 will be used for rendering but unless the right doctypes are used (XHTML and HTML5 specifically) IE will still fall back into quirks mode as needed. This should allow existing pages to continue to use the fallback engine while new pages that have the proper HTML doctype set can take advantage of the newest features.
Here's an example of how I set the registry keys in my Tarma Installmate registry configuration:
Note that I set all three values both under the Software and Wow6432Node keys so that this works regardless of where these EXEs are launched from. Even though all apps are 32 bit apps, the 64 bit (the default one shown selected) key is often used.
So, now once I've set the registry key for hh.exe I can now launch my CHM help file from Explorer and see the following CSS3 IE9 rendered display:
It sucks that we have to go through all these hoops to get what should be natural behavior for an application to support the latest features available on a system. But it shouldn't be a surprise - the Windows Help team (if there even is such a thing) has not been known for forward looking technologies. It's a pretty big hassle that we have to resort to setting registry keys in order to get the Web Browser control and the internal CHM engine to render itself properly but at least it's possible to make it work after all.
Using this technique it's possible to ship an application with a help file and allow your CHM help to display with richer CSS markup and correct rendering using the stricter and more consistent XHTML or HTML5 doctypes. If you provide both Web help and in-application help (and why not if you're building from a single source) you now can side step the issue of your customers asking: Why does my help file look so much shittier than the online help… No more!