As far as I know there is still no proper definition of the GSL (https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#faq51-is-githubcommicrosoftgsl-the-gsl). But it seems to me that it makes sense for the definition of span to follow what's being standarised for C++20.

gsl-lite::span doesn't support static extents (https://github.com/martinmoene/gsl-lite/blob/master/include/gsl/gsl-lite.hpp#L451), which is more strange given that:

• The Microsoft GSL implementation does support static extents (https://github.com/Microsoft/GSL/blob/master/include/gsl/span#L75)
• The gsl-lite limitation doesn't seem to be because of a lack of resources since span-lite does support static extents (https://github.com/martinmoene/span-lite/blob/master/include/nonstd/span.hpp#L496)