1.3.4 Parameter Names
Most formal parameter names consist of a lowercase prefix followed by one or more words, each beginning with a capital letter. The prefix indicates the parameter type, while the words that follow describe the parameter content. These prefixes are as follows:
Both the Service Provider and its client use 32-bit handles to represent the data structures they associate with devices. To distinguish these handles from one another at the TSPI level, an additional mnemonic convention is added to the "h" prefix used above. The handle representing a Service Provider (i.e., Device Driver) data structure is named with an "hd" prefix. The handle representing a client (i.e., TAPI DLL) data structure is named with an "ht" prefix. For example, a formal parameter named "hdLine" refers to the Service Provider's "line" data structure while "htLine" refers to the client's "line" data structure.
The Windows Telephony SPI is "32-bit ready". It uses 32-bit data types almost exclusively to make migration to the 32-bit version of Windows as easy as a recompile. DWORDs are used throughout and handles are 32 bits.