XSD Sequence of Choice

I want to write a schema which accept XML documents like this:

<plugin>
  <label text="blabla" />
  <line />
  <break />
  <textbox name="mytextbox" length="8" required="true" />
  <checkbox name="mycheckbox" checked="true" />
  <combobox name="mycombo">
    <option value="one">Option One</option>
    <option value="two" selected="true">Option One</option>
  </combobox>
  <break />
</plugin>

So I want the plugin to contain elements of set {combobox,checkbox,textbox,label,line,break}. I have written this XSD, but this is wrong:

<?xml version="1.0" encoding="utf-8"?>
<xs:schema id="NewDataSet" xmlns="" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
  <xs:element name="plugin">
    <xs:complexType>
      <xs:sequence>
       <xs:choice>
        <xs:element name="line" />
        <xs:element name="break" />
        <xs:element name="label">
          <xs:complexType>
            <xs:attribute name="text" type="xs:string" />
            <xs:attribute name="bold" type="xs:boolean" />
            <xs:attribute name="width" type="xs:positiveInteger" />
          </xs:complexType>
        </xs:element>
        <xs:element name="textbox">
          <xs:complexType>
            <xs:attribute name="name" type="xs:string" />
            <xs:attribute name="width" type="xs:positiveInteger" />开发者_JS百科
            <xs:attribute name="text" type="xs:string" />
            <xs:attribute name="length" type="xs:positiveInteger" />
            <xs:attribute name="required" type="xs:boolean" />
          </xs:complexType>
        </xs:element>
        <xs:element name="combobox">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="option" nillable="true" minOccurs="0" maxOccurs="unbounded">
                <xs:complexType>
                  <xs:simpleContent msdata:ColumnName="option_Text" msdata:Ordinal="2">
                    <xs:extension base="xs:string">
                      <xs:attribute name="value" type="xs:string" />
                      <xs:attribute name="selected" type="xs:boolean" />
                    </xs:extension>
                  </xs:simpleContent>
                </xs:complexType>
              </xs:element>
            </xs:sequence>
            <xs:attribute name="name" type="xs:string" />
            <xs:attribute name="width" type="xs:positiveInteger" />
          </xs:complexType>
        </xs:element>
        <xs:element name="checkbox">
          <xs:complexType>
            <xs:attribute name="name" type="xs:string" />
            <xs:attribute name="checked" type="xs:boolean" />
            <xs:attribute name="text" type="xs:string" />
            <xs:attribute name="width" type="xs:positiveInteger" />
          </xs:complexType>
        </xs:element>
       </xs:choice>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  <xs:element name="NewDataSet" msdata:IsDataSet="true" msdata:UseCurrentLocale="true">
    <xs:complexType>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element ref="plugin" />
      </xs:choice>
    </xs:complexType>
  </xs:element>
</xs:schema>

I have tested it with this validator tool...

but it says:

"cvc-complex-type.2.4.d: Invalid content was found starting with element 'line'. No child element is expected at this point."

So...What's wrong? I don't understand this message. What child elements at what point?

Your sequence definition only has one child, i.e. choice.

This means that plugin is only permitted one child, though it may be any one of the elements you have defined.

If you remove the choice element, leaving its content in situ, you will have a fixed sequence of elements that can be children of plugin.

If, instead, you remove the sequence element, leaving it's content in situ, and add an attribute to the choice element: maxOccurs="unbounded", then it should validate a plugin element with any number of the children you specify, in any order.

This will allow you to repeat the choice over and over in your sequence:

<xs:complexType>
  <xs:sequence>
   <xs:choice maxOccurs="unbounded">