There is a mechanism to custom open files in Smile depending on their file extension:

• If you want to handle the opening of the files of extension .xxx, you have to define in Smile' context a handler named customopen_xxx (replace xxx with the extension you are interested in). This handler has one parameter that is the file path.
• If this handler does not exists or if it fails, the default behavior occurs. Such a handler can perform tests to choose opening the file its own way or to fail to get the default opening behavior.
• You can have such handlers defined in your context additions.

For example, the following handler opens .html files in unicode windows, and add a contextual menu "open this file in Safari":

on customopen_html(f)
    set w to make new Unicode window with properties {path name:f}
    set script of w to "on CustomMenuItems(w)
    try
        set x to continue CustomMenuItems(w)
    on error
        set x to {}
    end try
    return {\"open this file in Safari\"} & x
end CustomMenuItems
on do menu acmd to w
    if acmd is \"open this file in Safari\" then
        try
            save w in 0
            set f to path name of w
            tell application \"Safari\" to open f
        end try
    else
        continue do menu acmd to w
    end if
end do menu"
end customopen_html