Documentation about abstract type declarations on assignments

[ArnoStrouwen]

https://docs.julialang.org/en/v1/manual/types/#Type-Declarations

When appended to a variable on the left-hand side of an assignment, or as part of a local declaration, the :: operator means something a bit different: it declares the variable to always have the specified type

But this does not seem to be true for abstract types:

b::Real = 1
b = 1.0
b = '1'
b = "1"

b does not have type Real, instead it can have any concrete subtype of Real.

[barucden]

My understanding of the documentation is that b::T = x ensures that b isa T will always hold.

In your example:

julia> b::Real = 1
1

julia> b = 1.0
1.0

julia> b isa Real
true

julia> b = '1'
'1': ASCII/Unicode U+0031 (category Nd: Number, decimal digit)

julia> b isa Real # even though  '1' isa Real == false
true

IIRC, any assignment to a variable declared as b::T translates to

b = convert(T, x)::T

[ArnoStrouwen]

My understanding of the documentation is that b::T = x ensures that b isa T will always hold.

IIRC, any assignment to a variable declared as b::T translates to
b = convert(T, x)::T

If it works like this, I think the docs would benefit from explicitly mentioning this.
The current phrasing is confusing to me.