Tarma Installer does not have an explicit search action for registry keys or values on the target system during installation. However, you can use symbolic expressions such as <@...regpath...> to check for the presence of a value. For example:
<@<HKLM>\Software\Microsoft\Windows\CurrentVersion\ProductId>
...retrieves that value. To retrieve the unnamed (default) value, end the path with a backslash, immediately before the closing '>', as in:
<@<HKLM>\Microsoft\Windows\CurrentVersion\App Paths\Tin.exe\>