More nits

[Murata Makoto <mura034@attglobal.net>]

1)

In 7.1, the production rule for singleAttributeGroup has <attribute> nameClass </attribute>.  
This is unnecessary because of 4.11.

2)

In the production rule for singleAttributeGroup,

<choice> (<empty/> | value) singleAttributeGroup </choice>

should read 

<choice> (<empty/> | singleAttributeGroup) singleAttributeGroup </choice>

3)

The definition of a non-terminal "params" is missing.  It should be replaced 
with param* and we can borrow a production from Section 4.

param   ::=   <param name="NCName"> string </param> 

Cheers,

Makoto