Attributes are used to change or consult properties of elements. Each element has a set of attributes that affect it, and each attribute can work differently for each element. Depending on the element, its value can be computed or simply verified. Also it can be internally stored or not.
Attribute names are always upper case, lower case names will not work. But attribute values like "YES", "NO", "TOP", are case insensitive, so "Yes", "no", "top", and other variations will work.
If not defined their value can be inherited from the parent container.