Using colon : or equality = to declare dict key-values

[th0ger]

It's confusing that dict key-values can be declared with either : or = and even mixed:

data = {
    key1 = "value1",
    key2 : "value2"
}

The tour uses examples with =, while the spec uses examples with :. But none of the docs really states the formal syntax, mentions the interchangeability, or states the preferred/recommended syntax.

In the code style section, there is the mixed example:

d1 = {labels: {k1 = "v1"}}

Here the colon : is referred to dict "instantiation" and equality = referred to as "override attribute operator". But it is unclear whether the difference is syntactical sugar or is functionally different.