I saw the T AG thing before in you tube. If I am correct, What that is, is like a link to your topic,picture,video,etc so if you posted a photo of your model structure and add tags of; model, N scale, structure,railroading, then if someone tries searching for videos,etc then your photo will come up in search if the user searched using one of these "keywords"
that's how I find Burlington Northern train video on you tube as most use trains or B N in their keywords list.
On a similar topic, that is how Google,etc search engines find websites. When you design your website, you have a command script (HTML coding) that you put in all the words that link to your subject. The search engines pick up these Meta links ( i think that was what they are called) So a p orn site is gonna have the whole dictionary in their meta link file so when you Google "fox" or "babe" or "railroads" then their site comes up in the results.
Dave
former website owner. Back when I was younger I had a Pam Anderson site of strictly pictures of her, nudes,normal shots, you name it. I couldn't tell ya how many sites i was kicked out of due to my graphic content (nudes)