This is from the JSON-LD spec.
ActivityPub / ActivityStream are based on JSON-LD.
I think it was a very bad idea for JSON-LD to define "number" this way!
It makes it so numbers with fractional values are inexact & lossy.
This include values that are common for money.
For example, neither 0.10 and 0.20 can be represented exactly. So, 0.10 + 0.20 does NOT equal 0.30!
It should have used FIXED-point numbers rather than FLOATING-point.
This is likely (directly or indirectly) the fault of a single paragraph in IETF RFC-7159 / RFC-8259 (shown in the attached screen-shot).
(And note that, there is a difference between JSON and IETF JSON. JSON did not have this. IETF JSON does.)
That paragraph (in the IETF RFC) was NOT a requirement. But, others made it a requirement — including JSON-LD.
There is a larger discussion about fixed-point numbers versus floating-point numbers.
And that, ALL programming-languages should have fixed-point numbers built into them.
And that, programmers should be warned against using floating-point numbers in all but a set of very specialized situations — where inexact math is OK.
For most programmers in most situations inexact math is NOT OK. And, they should NOT use floating-point numbers.
@reiver ⊼ (Charles) 