Usage of XML namespace prefix in the generated diagram documents

I was trying the BPMN online editor for the “What if you are hungry?” process. The exported BPMN diagram does not have XML namespace prefix for definitions tag. Later, I was working on a different process. When I exported that one, I could see that the tag as <bpmn:definitions ... IN case of former, I see there is a default xmlns definition to the same URI as that of bpmn prefix. So, I think, technically, documents are same. Nevertheless, I wanted to know if there is a predictability around when a tag is prefixed or not.

1st Case

<definitions xmlns="" xmlns:bpmndi="" xmlns:omgdi="" xmlns:omgdc="" xmlns:xsi="" id="sid-38422fae-e03e-43a3-bef4-bd33b32041b2" targetNamespace="" exporter="bpmn-js (" exporterVersion="8.8.0">

2nd case

<bpmn:definitions xmlns:xsi="" xmlns:bpmn="" xmlns:bpmndi="" xmlns:dc="" xmlns:di="" id="Definitions_16be12s" targetNamespace="" exporter="bpmn-js (" exporterVersion="8.8.0">