Default values for named parameters are documented using a `:` instead of `=`.

[lrhn]

See, e.g., https://api.dartlang.org/stable/2.6.1/dart-core/RegExp-class.html which contains

RegExp(String source, { bool multiLine: false bool caseSensitive: true @Since("2.4") bool unicode: false @Since("2.4") bool dotAll: false })

(missing commas aside, #2052).
The language allows, and recommends, using = to separate parameter and default value, so it would be prettier if the documentation used = as well.