How to use inputmodes property

I am working on a VoiceXML interpreter and I wonder how to interprete inputmodes property. When you find a inputmodes property with the value "dtmf" at the <field> level, is that mean that all voice grammars definied in higher scopes are disabled when you interprete that field ?
 
Thank you in advance for your help,
 
regards. 
 

 
Fabrice Mare
Telisma
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22300 Lannion
France
Tel: +33 (0)2.96.05.59.14
Fax: +33 (0)2.96.05.59.05
fmare@telisma.com
www.telisma.com <http://www.telisma.com/>