@Override
    protected void handleKeyValue(String attribute, String value) {
        // string() will point to the start of value.
        if (string().peek('[') && isMap) {
            // begin parsing MultiValueQueryTerm
            isMap = false;
            parseMultiValue(attribute);
            isMap = true;
        } else {
            handleAttribute(attribute, value);
        }
    }
Parses an attribute string on the format <code>{attribute:value, ...}</code>
where <code>value</code>' is either a single value or a list of values
<code>[value1,value2,...]</code>, and each of the values can have an optional
bitmap specified <code>value:bitmap</code>. <code>bitmap</code> can be either
a 64-bit hex number <code>0x1234</code> or a list of bits <code>[0, 2, 43,
22, ...]</code>.

@author Magnar Nedland
container-search/src/main/java/com/yahoo/search/querytransform/BooleanAttributeParser.java