XML Schema Part 1-{any attributes with non-schema namespace}

Hello:

in 3.3.2 XML Representation of Element Declaration Schema Components
 
XML Representation Summary: element Element Information Item
<element 
  abstract = boolean : false
  block = (#all | List of (extension | restriction | substitution)) 
  default = string 
  final = (#all | List of (extension | restriction)) 
  fixed = string 
  form = (qualified | unqualified)
  id = ID 
  maxOccurs = (nonNegativeInteger | unbounded)  : 1
  minOccurs = nonNegativeInteger : 1
  name = NCName 
  nillable = boolean : false
  ref = QName 
  substitutionGroup = QName 
  type = QName 
  {any attributes with non-schema namespace . . .}>
  Content: (annotation?, ((simpleType | complexType)?, (unique | key | keyref)*))
</element>

I don't know exactly "{any attributes with non-schema namespace . . .}" means, does it mean that I can add any attribute not listed in element defination, is it validate to define a element as follows:

<element name="a" type="string" action="add"/>



thanks,

xiangli zhang