public XMLWriter attribute(Utf8String name, AbstractUtf8Array value) {
        if (value.isEmpty()) return this;
        allowAttribute();
        return w(SPACE).w(name).w(ATTRIBUTE_START).w(value).w(ATTRIBUTE_END);
    }
Writes an attribute by its utf8 value

@param name the name of the attribute. An exception is thrown if this is null
@param value the value of the attribute. This method does nothing if the value is null or empty
vespajlib/src/main/java/com/yahoo/text/XMLWriter.java