As

It's a reserved word typically used with the do command to specify a scripting language.

do field 1 as "Javascript"

Used also with the export command to specify the file format to export to, used with the go command to specify the mode of a stack; used with the save command to specify the file name and location.

export image "image" to file myFile as PNG

go stack "Controls" as palette

save this stack as "../Backups/Current.rev"