What is meaning/difference of Level 2 and Level 1 in XMLHttpRequest document provided by W3C
what is that Level No represents in that W3c provided document?
When a specification is developed at W3C, multiple major revisions of different maturity can exist simultaneously. So for example Level 1 could be the more mature version (closer to becoming a Recommendation), and Level 2 might define more features, but be further away from becoming a REC.
In the specific case of XHR (based on the "Specification history" section of the spec):
W3C XMLHttpRequest Level 1 was an attempt to push the description of the functionality already implemented by MS Internet Explorer (and copied by other browsers) through the W3C Process, designed to:
- support multiple specification development methodologies
- maximize consensus about the content of stable technical reports
- ensure high technical and editorial quality
- promote consistency among specifications
- facilitate royalty-free, interoperable implementations of Web Standards, and earn endorsement by W3C and the broader community.
Since the process of becoming a W3C recommendation is rather slow, most improvements that were yet to be implemented were defined in a separate document, W3C XMLHttpRequest Level 2, which was intended to become a W3C Recommendation later than Level 1 and to eventually supersede the Level 1 version.