sfref is an attribute that we use to resolve dynamic links. Its value is [Provider]Guid - this shows the data provider and the item ID. When the content is saved or edited we call LinkParser.ResoveLinks and pass the entire HTML of the content item. We check for this attribute and its value. Then we set the proper href if the item is found.
To perform a check to see what might be the outcome if we remove the sfref, insert two images into the content block and then in HTML mode strip out the sfref from one image and keep the sfref for the other image and save, re-open the editor and go to HTML editor and see the difference of the two image tags, the image tag in which the sfref was removed, now has the full path / absolute path
of the image location in the src value and the other image tag is having the relative path
of the image in the src value. Now if we move those images to another library and go back to the page and open the content editor and open the html editor and see the image which has the sfref is automatically changed the src value to the new location of relative path but the other one still has the old full path but still the image might be visible with the wrong path as the browser may be cached that one, but will be a problem after the project deployed to another location.
So, If the sfref attribute is stripped out then the item url will not be resolved properly and when we rename/relocate the content item( image, document etc) this will break the link.
Please read the blog of Stanislav Velikov (though this blog is related to the old version) which may help to get more idea on this issue here: http://www.sitefinity.com/blogs/stanislav-velikovs-blog/2013/02/15/dynamically-resolving-sitefinity-links-when-using-htmlfield
And also please read the following forum to get more ideas on this issue: http://www.sitefinity.com/developer-network/forums/developing-with-sitefinity/change-in-sfref-value-causes-to-image-to-fail
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