Can you explain these shared macros?

[btgvesta]

Can you explain these macros ?

#define StringZ(Z) {sizeof(Z) - 1, (u8 *)(Z)}
#define StringZFunc(Z) BundleString(sizeof(Z) - 1, (Z))

[bagaffey]

Yes, those functions are basically initializing the string (alias buffer) struct without copying anything.
So, this:

typedef struct buffer
{
    umw Count;   // strength length
    u8* Data;    // the string data
} buffer, string;

StringZ is creating the struct initialization at compile time. This should only be used for literals. I am actually going to rename this now to make it clearer.
StringZFunc creates it at runtime because there is a function call happening.

Both simply take a string argument. One should be used for literals while the other could be used for runtime strings.

The Z in the name is to indicate that it handles zero-terminated strings, that means a string that is terminated C-style with a null at the end \0.

The length that is calculated is the logical length.