public boolean isTrue(String key) {
        return h.isTrue(key);
    }
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
application/src/main/java/com/yahoo/application/container/handler/Headers.java