associate self attribute or uniqueId of a rectangle in spread xml to extendscript rectangle

Hi, i am using extendscript to export my indesign document to html. in that process i am trying to assign a uniquer attribute to certain images that can be indentfied in HTML later. also i need to tie this back to the Rectangle/image tag that is generated from idml. the xml tags have Self attributes but i cannot access them in extend script as the property is not avaiable. 

briefly put, i have a process that generates the idml and unpacks it. i am workging on another process that will generate the html using extend script. i somehow need to tie back specific images generated in html to the tags that are in the spread_abc.xml. as of now i only see self attribute that is unique in xml, but it is not avaiable as a property on the object. in extendscript we have id which is integer. any help is appreciated

or is there a way to read the value of uniqueId in extendscript.