: All about SEO Meta Tag Layout Most of the meta tag to the importance we draw closer to Google SEO, but also be friendly to these search engines Bing MSN, DMOZ, Yahoo. Looking at google

Most of the meta tag to the importance we draw closer to Google SEO, but also be friendly to these search engines Bing MSN, DMOZ, Yahoo.

Looking at google I have taken the first four pages of the first results by studying their SEO structure.

To surprise I found three types of titles on the same page.

<title>Agencia Multimedia móviles iPhone Android.</title>
<meta name="title" content="Agencia Multimedia móviles iPhone Android.">
<meta property="og:title" content="Agencia Multimedia móviles iPhone Android.">

I found three types of meta description on the same page to surprise one of them in English and Spanish.

<meta name="description" lang="en" content="Agency Multimedia iPhone Android Mobile.">
<meta name="description" content="Agencia Multimedia móviles iPhone Android.">
<meta property="og:description" content="Agencia Multimedia móviles iPhone Android.">

The canonical URL note showing in the same place two identical specifications.

<link rel="canonical" href="https://blog.example.com/dresses/green-dresses-are-awesome" />
<meta property="og:url" content="https://blog.example.com/dresses/green-dresses-are-awesome">

Like other types of meta tags that are very relevant and interesting, all this taken from the first four pages of the first results.

<meta name="theme-color" content="#009587">
<meta name="msapplication-TileColor" content="#009587">
<meta property="og:image" content="http://www.example.com/themes/dejabu/images/og_logo.png">
<meta property="og:site_name" content="Proun New Media Agency">
<meta name="author" content="Multi Estudio">
<meta name="revisit-after" content="10-days">
<meta name="robots" content="all/index/follow">
<meta content="global" name="distribution">
<meta name="language" content="spanish">
<meta name="copyright" content="Copyright © 2014 Multi Studio All rights reserved.">

My question:

In a product or brand overall structure seo multi language should be used in the basic HTML structure?

<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>

</body>
</html>

What is the difference between name="og:title" name="DC.title" ?

Of all the meta tag them understand mentioned as the main Google search engine, Bing MSN, DMOZ, Yahoo?

The importance of tags h1, h2, h3, h4, h5, h6 h1 How many can be repeated on the same page as the other labels?