[1] If I take a quick tour to w3.org schema spec., there is this.
[tt]quote
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) : [blue]1[/blue]
minOccurs = nonNegativeInteger : [blue]1[/blue]
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>
[/tt]
The two "1" are meant for default value.
[2]
><foobar />
>is that the equivalent of an occurance of once or no occurance?
It counts as once.