Flow type, What does the `+` symbol mean in front a property?

Question

I came across the following code written in js FlowType (I am interested to know the value of + in the context of FlowType not in general JS).

Could you please expla

Answer 1

The + symbol in front of the property means the property is read-only

Reference: https://flow.org/en/docs/types/interfaces/#toc-interface-property-variance-read-only-and-write-only