public boolean isTrue(String key) {
        List<String> lst = content.get(key);
        if (lst == null) {
            return false;
        }
        for (String value : lst) {
            if (!Boolean.valueOf(value)) {
                return false;
            }
        }
        return true;
    }
Convenience method for checking whether a named header field is <em>true</em>. To satisfy this, the
header field needs to have at least 1 entry, and Boolean.valueOf() of all its values must parse as
<em>true</em>.

@param key the key whose values to parse as a boolean.
@return the boolean value of the named header.
jdisc_core/src/main/java/com/yahoo/jdisc/HeaderFields.java