/proc/length(object)
Arguments:
object: A string, a list or a file.
Returns:
number, null: The length of the provided object.
world.log << length("Hello, world!") // 13, number of characters

world.log << length(list("Hello,", " world!")) // 2, number of elements in the array
Parity Issue ⚠️
The BYOND implementation of DreamMaker also allows you to check the length of a file, such as:
world.log << length(file("foo.txt"))

For non-ASCII strings, you can use the length_char() variant of this proc to correctly handle unicode, which works with character counts.