doc tweak

Author: ablaom

docs/src/accessor_functions.md

@@ -17,8 +17,8 @@ The sole argument of an accessor function is the output, `model`, of [`fit`](@re
 
 ## Implementation guide
 
-All new implementations must implement [`LearnAPI.algorithm`](@ref). All others are
-optional. All implemented accessor functions must be added to the list returned by
+All new implementations must implement [`LearnAPI.algorithm`](@ref). While, all others are
+optional, any implemented accessor functions must be added to the list returned by
 [`LearnAPI.functions`](@ref).