```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>WBC (Group:WBC)@13:31:51</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>4</hlevel>
            <item_name>WBC (Group:WBC)</item_name>
            <item_key>\\i2b2_LABS\i2b2\Labtests\LAB\(LLB53) Hematology\(LLB57) Complete Blood Count\WBC\</item_key>
            <item_icon>FA</item_icon>
            <tooltip>Labtests \ Hematology \ Complete Blood Count \ WBC (Group:WBC)</tooltip>
            <class>ENC</class>
            <constrain_by_value>
                <value_operator>EQ</value_operator>
                <value_constraint>H</value_constraint>
                <value_type>FLAG</value_type>
            </constrain_by_value>
            <item_is_synonym>false</item_is_synonym>
        </item>
    </panel>
</ns4:query_definition>

```

I want to find all instances where the lab test result for WBC (White Blood Cell Count) is equal to the value 'H' in the category of hematology under the group WBC, with any timing, and the specificity scale set to 0, accuracy scale set to 100, and panel number and timing set to 1. This query is designed to search for WBC values in the i2b2 database with a high level of precision and accuracy, using the specified constraints.