On mouse down in thumb, issue SB_THUMBTRACK with current position.
[wine] / tools / winapi_check /
drwxr-xr-x   ..
-rw-r--r-- 6227 modules.dat
-rw-r--r-- 7841 modules.pm
-rw-r--r-- 1872 nativeapi.dat
-rw-r--r-- 4697 nativeapi.pm
-rw-r--r-- 4080 preprocessor.pm
-rwxr-xr-x 19963 winapi_check
-rw-r--r-- 6800 winapi_documentation.pm
-rw-r--r-- 10759 winapi_function.pm
-rw-r--r-- 1924 winapi_global.pm
-rw-r--r-- 13581 winapi_local.pm
-rw-r--r-- 16518 winapi_parser.pm