This checks the three variables (SCRIPT_NAME, REQUEST_URI, and SCRIPT_FILENAME) to see if the subpath is already present before adding it. For SCRIPT_NAME and REQUEST_URI it explicitly checks to see if the string begins with the subpath. For SCRIPT_FILENAME, it just checks to see if the subpath is present within the string (this seems like it could be prone to error if a short or common string is chosen for the subpath).
This checks the three variables (SCRIPT_NAME, REQUEST_URI, and SCRIPT_FILENAME) to see if the subpath is already present before adding it. For SCRIPT_NAME and REQUEST_URI it explicitly checks to see if the string begins with the subpath. For SCRIPT_FILENAME, it just checks to see if the subpath is present within the string (this seems like it could be prone to error if a short or common string is chosen for the subpath).