Macro xml5ever::namespace_url

macro_rules! namespace_url {
    ("http://www.w3.org/2000/xmlns/") => { ... };
    ("") => { ... };
    ("http://www.w3.org/2000/svg") => { ... };
    ("http://www.w3.org/XML/1998/namespace") => { ... };
    ("http://www.w3.org/1999/xlink") => { ... };
    ("*") => { ... };
    ("http://www.w3.org/1998/Math/MathML") => { ... };
    ("http://www.w3.org/1999/xhtml") => { ... };
}

Takes a namespace url string and returns its key in a string cache.