SF.2 allow inline variables and static inline class member variables

SF.2 has a list under "A header file must contain only" that does not include:

• static inline class member variables (not just functions)
• inline variables not in a class declaration (again, not just functions)

Both are supported since C++17, resulting in all translation units linking the entity to the same memory location, The first point above results in code simplification and allows implementation of header-only classes that would otherwise not be possible. In [https://en.cppreference.com/w/cpp/language/inline](inline specifier - cppreference.com):

An inline function or variable(since C++17) ... has the same address in every translation unit.

For example, if a header includes:

class MyClass
{
    public:
        static inline int staticInlineMember = 5;
};
inline int inlineVariable = 5;

The memory location of staticInlineMember is always the same, when that header is included in multiple source files. So is the location of inlineVariable.

Start by locating the SF.2 guideline and reviewing the section listing what a header file may contain, then compare its wording with the C++17 inline-variable rules referenced in the issue. Done means the guideline explicitly addresses both static inline class member variables and non-member inline variables without narrowing the existing guidance.