A quick explanation of the differences between gsl::span and std::span

gsl::span-and-std::span.md

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+# Span 
+## What is span
+A span is a view over memory. It does not own the memory and is only a way to access contiguous sequences of objects. 
+
+The `gsl::span` is based on the standardized version of `std::span` which was added to C++20. Originally, the plan was to deprecate `gsl::span` when `std::span` finished standardization, however that plan changed when the runtime bounds checking was removed from `std::span`'s design.
+
+## Differences between `gsl::span` and `std::span`
+The only difference between `gsl::span` and `std::span` is that `gsl::span` strictly enforces runtime bounds checking. Any violations of the bounds check results in termination of the program.
+
+## Which version of span should I use?
+### Use gsl::span if:
+- you want to guarantee bounds safety in your project. 
+  - All data accessing operations use bounds checking to ensure you are only accessing valid memory.
+- your project uses C++14 or C++17.
+  - `std::span` as it was not introduced into the STL until C++20.
+### Use `std::span` if:
+- your project is C++20 and you need the performance offered by `std::span`.
+
+# span_iterator
+Like `gsl::span`, `gsl::span`'s iterators also differ from `std::span`'s iterator in that all access operations are bounds checked.