```xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns4:query_definition xmlns:ns2="http://www.i2b2.org/xsd/cell/crc/psm/1.1/" xmlns:ns4="http://www.i2b2.org/xsd/cell/crc/psm/querydefinition/1.1/" xmlns:ns3="http://www.i2b2.org/xsd/cell/crc/psm/analysisdefinition/1.1/">
    <query_name>Principal Diagn@13:49:35</query_name>
    <query_timing>ANY</query_timing>
    <specificity_scale>0</specificity_scale>
    <panel>
        <panel_number>1</panel_number>
        <panel_timing>ANY</panel_timing>
        <panel_accuracy_scale>100</panel_accuracy_scale>
        <invert>0</invert>
        <total_item_occurrences>1</total_item_occurrences>
        <item>
            <hlevel>5</hlevel>
            <item_name>Acute pancreatitis</item_name>
            <item_key>\\i2b2_DIAG\i2b2\Diagnoses\Digestive system (520-579)\Other diseases of digestive system (570-579)\(577) Diseases of pancreas\(577-0) Acute pancreatitis\</item_key>
            <item_icon>FA</item_icon>
            <tooltip>Diagnoses \ Digestive system \ Other diseases of digestive system \ Diseases of pancreas \ Acute pancreatitis</tooltip>
            <class>ENC</class>
            <constrain_by_modifier>
                <modifier_name>Principal Diagnosis</modifier_name>
                <modifier_key>\\i2b2_DIAG\Principal Diagnosis\</modifier_key>
                <applied_path>\i2b2\Diagnoses\Digestive system (520-579)\%</applied_path>
            </constrain_by_modifier>
            <item_is_synonym>false</item_is_synonym>
        </item>
    </panel>
</ns4:query_definition>

```

I want to find all instances where 'Acute pancreatitis' is the principal diagnosis in the 'Digestive system' category under 'Diseases of pancreas' section. The specificity scale is set to 0, meaning the diagnosis is not restricted to a specific time frame, and the panel accuracy scale is set to 100, indicating that the diagnosis must be accurate. This query will return only one item with the specified condition.