Where is <title> tag generated?

[epogrebnyak]

Is the title tag added as a part of Jekyll own work, not through the theme layout? What code is reposnsible for <!-- Begin Jekyll SEO tag v2.6.1 -->1

This would help better solve #40

<!-- Begin Jekyll SEO tag v2.6.1 -->
<title>Custom header 1</title>
<meta name="generator" content="Jekyll v3.9.0" />
<meta property="og:title" content="Custom header 1" />
<meta property="og:locale" content="en_US" />
<meta name="description" content="Where does a short description of my site’s purpose go?" />
<meta property="og:description" content="Where does a short description of my site’s purpose go?" />
<link rel="canonical" href="https://epogrebnyak.github.io/never-blog-again/" />
<meta property="og:url" content="https://epogrebnyak.github.io/never-blog-again/" />
<script type="application/ld+json">
{"@type":"WebSite","headline":"Custom header 1","url":"https://epogrebnyak.github.io/never-blog-again/","description":"Where does a short description of my site’s purpose go?","@context":"https://schema.org"}</script>
<!-- End Jekyll SEO tag -->

[epogrebnyak]

Appareantly <title> is generated by https://github.com/jekyll/jekyll-seo-tag/
and in https://github.com/pages-themes/primer/blob/75e726cad88159d618ae58ed588d6b9c1fdfc6aa/_layouts/default.html there is :

{% seo %}

Hard to say how name is recyled by jekyll-seo-tag, but @seshrs confirmed it appears is <title>, when title is null