Calculate the difference between two nodes

Is it possible to find the difference two nodes and use the that difference as a constraint for a particular control.

<xforms:bind id="DebitRebate1"
    nodeset="instance('charge-options-setup')/Pattern_Setup1/Pattern1/DebitRebate1"
    type="xforms:d开发者_C百科ouble" 
    constraint=". &lt; instance('charge-options-setup')/Pattern_Setup1/Pattern1/DebitPrice1
                and instance('charge-options-setup')/Pattern_Setup1/Pattern1/DebitPrice1-. &gt;
                instance('charge-options-setup')/Locations_Patterns/Debit_Minimum_Margin"/>

Yes, you can use the difference between two nodes as a constraint on another node, and the code you quote seems about right. Just a couple of comments:

• In your XPath, instead of < and > you can use just lt and gt. This performs a value comparison, and makes the expression easier to read.
• Also make sure you have spaces around node named: instead of DebitPrice1-. use DebitPrice1 - .. This is necessary, as - can be used as part of an element or attribute name, so foo-bar point to <foo-bar> not what's in <foo> minus what's in <bar>.