Merge pull request #21353 from JuliaLang/jb/fix21352

fix #21352, update dev docs on type specificity

doc/src/devdocs/types.md

@@ -486,10 +486,10 @@ mysubtype(Tuple{Array{Int,2}, Int8}, Tuple{Array{T}, T} where T)
 ## Subtyping and method sorting
 
 The `type_morespecific` functions are used for imposing a partial order on functions in method
-tables (from most-to-least specific). Note that `jl_type_morespecific(a,b)` really means "is `a`
-at least as specific as `b`?" and not "is `a` strictly more specific than `b`?"
+tables (from most-to-least specific). Specificity is strict; if `a` is more specific than `b`,
+then `a` does not equal `b` and `b` is not more specific than `a`.
 
-If `a` is a subtype of `b`, then it is automatically considered more specific.
+If `a` is a strict subtype of `b`, then it is automatically considered more specific.
 From there, `type_morespecific` employs some less formal rules.
 For example, `subtype` is sensitive to the number of arguments, but `type_morespecific` may not be.
 In particular, `Tuple{Int,AbstractFloat}` is more specific than `Tuple{Integer}`, even though it is