We want to have the root element to be named "AAA", from null namespace and empty. The empty element is defined as a "complexType" with a "complexContent" which is a restriction of "anyType", but without any elements.

To specify, that element must be empty, use the "empty" element.

We want to have the root element to be named "AAA", from null namespace and containing text only.

To specify, that element contains text, use the "text" element.

We want to have the root element to be named "AAA", from null namespace and contains text and an element "BBB". You will need to set the attribute "mixed" to "true" - to allow mixed content.

Use the "interleave" pattern.

We want to have the root element to be named "AAA", from null namespace and contains one "BBB" and one "CCC" element. Their order is not important.

Use the "interleave" pattern.

We want to have the root element to be named "AAA", from null namespace and contains one "BBB" element, followed by one "CCC" element. Use the "sequence" pattern to specify exact order of the elements. The attributes "minOccurs" and "maxOccurs" are not necessary, because their default value is 1.

You need not to use any pattern, because the order is implicitly important - it's quite intuitive: if you do not specify otherwise, you want the elements to appear in the same order as you put them in your schema.

We want to have the root element to be named "AAA", from null namespace and contains a mixture of any number (even zero) of "BBB" and "CCC" elements. You need to use the trick below - use "sequence" element with "minOccurs" attribute set to 0 and "maxOccurs" set to "unbounded", and the attribute "minOccurs" of the "element" elements must be set to 0 too.

We will use the "interleave" and "zeroOrMore" patterns.

We want to have the root element to be named "AAA", from null namespace and contains either "BBB" or "CCC" elements (but not both). Use the "choice" element.

We will use the "choice" patterns.

We want to have the root element to be named "AAA", from null namespace and contains two patterns in any order. The first pattern is a sequence of "BBB" and "CCC" elements, the second one is a sequence of "XXX" and "YYY" element. The element "choice" allows one of the cases: either the sequence "myFirstSequence"-"mySecondSequence" or "mySecondSequence"-"myFirstSequence".

The element "choice" allows one of the cases: either the sequence "myFirstSequence"-"mySecondSequence" or "mySecondSequence"-"myFirstSequence".

This should be a simple task - we want the element "root" to contain text only and have just one attribute, named "xx".