The terms H1, H2, H3, H4, H5, H6 (upper or lower case) all refer to headers. Sometimes but not always they refer to the HTML version of the header, but in this document it simply refers to their semantici importance. And H1 header is more important than an H3, which is more important than an H6.
A header is a headline in the document. The lower the number, the more important the header. They have semantic meaning. Your audience, search engines, and screen readers are meant assign the most importance to an H1, less to an H2, and so on. HTML only recognizes levels 1 to 6. It's good writing practice to assign importance only to levels 1-3.
Headers are represented in Markdown like this:
# This is an H1, It's most important.
Normal body text.
## This is an H2. It's less important.
More body text.
### An H3 is about as low as you should go
Readers only absorb about 3 levels of importance.See also H1, H2, H3, H4, H5, H6.
The original formatting used on VuePress documents. It is an extended version of markup devised on the blog daring fireball. Its name is a humorous take on the term markup.
Special characters starting lines or surrounding phrases are converted to formatting or links.
For example, a line consisting # Welcome gets converted to
just the world Welcome but it's formatted as an HTML header, so it
will appear different from body text. In this document, it is
normally synonomous with markup.
In general, markup in the computer world means a way of representing text that also includes a way to transform that text. HTML is a good exampe of markup.
Normally in this document it refers to the original formatting used on VuePress documents. Special characters starting lines or surrounding phrases are converted to formatting or links.
For example, in VuePress a line consisting # Welcome gets converted to
just the world Welcome but it's formatted as an HTML header, so it
will appear different from body text. In this document, it is
normally synonomous with markdown, which is an extended
version of markup.
See the Markdown chapter.
The page title appears in your browser and is defined either by the first header on the page or using YAML. It's different from the site title, which appears on all pages if defined.
The site title appears on every page if you've configured it. The Vuepress default theme appends it to the page name in browser titles if it's been defined using config.js. The site title is different from the page title.