Fix manual about propagation of missing values (JuliaLang#35264)

doc/src/manual/missing.md

@@ -11,11 +11,11 @@ and behaves like them in most situations.
 
 ## Propagation of Missing Values
 
-The behavior of `missing` values follows one basic rule: `missing`
-values *propagate* automatically when passed to standard operators and functions,
-in particular mathematical functions. Uncertainty about the value of one of the operands
-induces uncertainty about the result. In practice, this means an operation involving
-a `missing` value generally returns `missing`
+`missing` values *propagate* automatically when passed to standard mathematical
+operators and functions.
+For these functions, uncertainty about the value of one of the operands
+induces uncertainty about the result. In practice, this means a math operation
+involving a `missing` value generally returns `missing`
 ```jldoctest
 julia> missing + 1
 missing
@@ -31,12 +31,17 @@ As `missing` is a normal Julia object, this propagation rule only works
 for functions which have opted in to implement this behavior. This can be
 achieved either via a specific method defined for arguments of type `Missing`,
 or simply by accepting arguments of this type, and passing them to functions
-which propagate them (like standard operators). Packages should consider
+which propagate them (like standard math operators). Packages should consider
 whether it makes sense to propagate missing values when defining new functions,
 and define methods appropriately if that is the case. Passing a `missing` value
 to a function for which no method accepting arguments of type `Missing` is defined
 throws a [`MethodError`](@ref), just like for any other type.
 
+Functions that do not propagate `missing` values can be made to do so by wrapping
+them in the `passmissing` function provided by the
+[Missings.jl](https://github.com/JuliaData/Missings.jl) package.
+For example, `f(x)` becomes `passmissing(f)(x)`.
+
 ## Equality and Comparison Operators
 
 Standard equality and comparison operators follow the propagation rule presented