A-keywords, which are also referred to as "associative keywords" (that's what the A stands for), tend to get neglected because most people believe they are too difficult to understand or use. Actually, they not as complicated as many people believe.
A-keywords are available in HTML Help CHM files only
A-keywords are a proprietary Microsoft technology that is only supported in the Microsoft HTML Help CHM format. They used to be supported in the Winhelp HLP format as well, but that is now obsolete and no longer used. Currently, you cannot use A-keywords in any other format.
A-keywords are only used for calls to CHM files
The only remaining purpose for A-keywords is for context calls to CHM files made from Windows applications.
A-keywords are used for "fuzzy" calls to CHM files
Unlike topic IDs and help context numbers, A-keywords can be "fuzzy", and multiple topics can contain the same A-keyword. The A stands for "associative" and means that you can make calls that locate all topics that are "associated" with that keyword.
A CHM context call to an A-keyword can include one or more A-keywords and optionally also a fallback topic. If topics containing the called keywords are found the the CHM viewer displays a list of links to choose from, otherwise the fallback topic is displayed.
Contrast topic ID calls and context number calls
•Topic IDs: When you link to a CHM topic from your application using the topic ID you always link directly to that topic. It is a single, hard-wired channel directly to that topic and none other.
•Context numbers: Help context numbers are also hard-wired to a single topic, with the difference that a single topic or anchor can have multiple context numbers. You can thus call the same topic with different numbers, which can be useful if you already have calls set up in your application to specific numbers.
A-keywords are invisible to the user
A-keywords are similar to ordinary index keywords but they are never seen by the user. They are only used for the associative CHM calls from your application that locate all the topics associated with that keyword.
About calls to A-keywords
See About A-keywords for background information and consult the HTML Help CHM API reference in the help of Microsoft HTML Help Workshop for details on the calling syntax. However, how the calls are made in your specific programming language will depend on the implementation in that language. You will need to consult your IDE and language documentation for the specifics.
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