How are Open Graph og:see_also tags intended to behave in Facebook?

Question

I've implemented og:see_also into my posts, but when they're liked, no additional webpages appear.

Is there specific criteria that needs to be met (i.e. do they require a specific og:type)? Must they be placed in a specific place within the Open Graph Meta Tag order?

Here's how they're set up:

<meta property="og:see_also" content="http://mywebsite.com/article1/">
<meta property="og:see_also" content="http://mywebsite.com/article2/">

They're displayed appropriately in the FB Debugger Tool. I'm just wondering if perhaps I may be doing something wrong, or if the see_also articles will only appear intermittently?

Here's the full code:

<meta property="og:site_name" content="SITE NAME"> 
<meta property="og:url" content="http://THEWEBPAGE.COM">
<meta property="og:title" content="TITLE">
<meta property="og:image" content="http://IMAGE-HERE.com">
<meta property="og:image:secure_url" content="https://IMAGE-HERE.com">
<meta property="og:image:type" content="image/jpg">
<meta property="og:image:width" content="300">
<meta property="og:image:height" content="300">

<meta property="og:description" content="DESCRIPTION">
<meta property="og:see_also" content="http://mywebsite.com/article1/">
<meta property="og:see_also" content="http://mywebsite.com/article2/">

Answer 1

The official OpenGraph protocol page doesn't mention anything about og:see_also, and Facebook's documentation doesn't do anything with it.

However, Pinterest mentions it, which suggests it may one of the og: tags Pinterest has extended from the standard. The only description we get is:

URL pointing to other related articles from the same domain. Up to 6 og:see_also tags can be provided.

Presumably, this tag would only have an effect when Pinterest users "pin" your page and get a "Rich Pin" out of it, which is a feature you'd have to apply for.