What is the "m=" attribute in a html tag? (Plus tons of other attributes found in bing result source) -

What is the "m=" attribute in a html <a> tag? (Plus tons of other attributes found in bing result source) -

so looking through source bing images search result, , seems html each hyperlink each returned image similar to:

<a href="#" ihk="hn.607992005913609849" m="{ns:&quot;images&quot;,k:&quot;5064&quot;,mid:&quot;3d11808868db7b3bd88719756eece65700723f87&quot;,surl:&quot;http://www.absoluteanime.com/naruto/kakashi.htm&quot;,imgurl:&quot;http://www.absoluteanime.com/naruto/kakashi.jpg&quot;,oh:&quot;225&quot;,tft:&quot;43&quot;,dls:&quot;images,5431&quot;,oi:&quot;http://www.absoluteanime.com/naruto/kakashi.jpg&quot;}" mid="3d11808868db7b3bd88719756eece65700723f87" onclick="return false;" t1="kakashi hatake" t2="640 x 480 · 32 kb · jpeg" t3="www.absoluteanime.com/naruto/kakashi.htm" h="id=images,5064.1" >

now, looking @ w3schools documentation <a> tag here, there doesn't seem documentation of these attributes, , after decently extensive googling , irc lurking can't find info on them.

am misunderstanding these things, i.e not attributes? (i relatively new html) or there somehow ton more attributes out there commonly documented?

i interested in m attribute because seems part of the <a> tag contains url of original image (as opposed bing's thumbnail).

in short, these custom attributes.

html tags allow set custom attributes on them , browsers ignore ones not understand.

some sample usages of feature in current utilize are:

to store meta-data libraries angularjs utilize them create directives

html