Technical Overview
MSAA is based on the Component Object Model (COM). COM defines a mechanism for applications and operating systems to communicate.
Figure 1 shows a high-level architecture of MSAA.
Applications (e.g., word processor) are called Servers in MSAA because they provide, or serve, information about their user interfaces (UI). Accessibility tools (e.g., screen readers) are called Clients in MSAA because they consume and interact with UI information from an application.
The system component of the MSAA framework, Oleacc.dll, aids in the communication between accessibility tools (clients) and applications (servers). The code boundary indicates the programmatic boundaries between applications that provide UI accessibility information and accessibility tools that interact with the UI on behalf of users. The boundary can also be a process boundary when MSAA clients have their own process.
The UI is represented as a hierarchy of accessible objects; changes and actions are represented as WinEvents.
Read more about this topic: Microsoft Active Accessibility
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