message: doc: Mention Span in developer-notes.md
diff: @@ -620,6 +620,19 @@ class A
  - *Rationale*: Easier to understand what is happening, thus easier to spot mistakes, even for those
  that are not language lawyers.
  +- Use `Span` as function argument when it can operate on any range-like container.
  +
  + - *Rationale*: Compared to `Foo(const vector<int>&)` this avoids the need for a (potentially expensive)
  + conversion to vector if the caller happens to have the input stored in another type of container.
  + However, be aware of the pitfalls documented in [span.h](../src/span.h).
  +
  +```cpp
  +void Foo(Span<const int> data);
  +
  +std::vector<int> vec{1,2,3};
  +Foo(vec);
  +```
  +
  - Prefer `enum class` (scoped enumerations) over `enum` (traditional enumerations) where possible.
  - *Rationale*: Scoped enumerations avoid two potential pitfalls/problems with traditional C++ enumerations: implicit conversions to `int`, and name clashes due to enumerators being exported to the surrounding scope.
  