21.1.1.1 String ( value = "" ):
21.1.2 Properties of the String Constructor:
There are two identical definitions for the "length" property, only one is needed.
I'm inclined to leave the redundancy in this case. There are two different conventions colliding here. One is that Properties of the * Constructor section typically state the value of the length property of the constructor. The other is that for functions with optional arguments we typically explicitly state the value of the their length property when specifying the function.
Both apply in this case. Depending upon their context, a reader who knows these conventions might choose either of these paths to look up the length and be mislead if they didn't find it.