# Hypertext Markup Language (HTML)
# Can I Use?
Before adding a new technology or technique to a website, it’s often worth checking to see how widespread the support for that technology is : The Can I Use ( https://caniuse.com/ ) website keeps up to date on what works in which browsers and version.
# Accessibility (a11y)
One key in understanding accessibility tools is to understand the standards to which the tool was developed. When deciding which accessibility tool will work best for you it is important to consider the standards and guidelines used by the different accessibility evaluation tools. The current standard is the Web Content Accessibility Guidelines version 2.1 (“WCAG 2”).
# WCAG 2
WCAG 2 (currently in version 2.1) consists of three priority levels that act as an industry standard. The first level, Level A, covers items on web pages that must be made accessible in order for individuals with disabilities to access the content at all. The second level, Level AA, includes items on web pages that should be made accessible to allow a wider group of users to access the content. Level AAA describes items on web pages that can be made accessible to allow the widest amount of individuals with disabilities to use the site..
# Section 508
Prior to January 2018, Section 508 of the United States Rehabilitation Act outlined a separate set of requirements for making federally-funded web sites accessible. Section 508 still requires accessibility, but now uses WCAG 2.0 (the predecessor to WCAG 2.1) Level A and AA as its benchmark.
Testing tools that report only on Section 508 standards are outdated.
# HTML5
HTML5 is the latest evolution of the standard that defines HTML. The term represents two different concepts. It is a new version of the language HTML, with new elements, attributes, and behaviors, and a larger set of technologies that allows the building of more diverse and powerful Web sites and applications. This set is sometimes called HTML5 & friends and often shortened to just HTML5.
# Twig/Jinja
Twig is both designer and developer friendly by sticking to PHP's principles and adding functionality useful for templating environments.
# Frameworks (Bootstrap)
Bootstrap is an open source toolkit for developing with HTML, CSS, and JS. Quickly prototype your ideas or build your entire app with our Sass variables and mixins, responsive grid system, extensive prebuilt components, and powerful plugins built on jQuery.
# CSS Box Model
Everything in CSS has a box around it, and understanding these boxes is key to being able to create layouts with CSS, or to align items with other items. In this lesson, we will take a proper look at the CSS Box Model so that you can build more complex layout tasks with an understanding of how it works and the terminology that relates to it.
# Flexbox
Flexbox is a one-dimensional layout method for laying out items in rows or columns. Items flex to fill additional space and shrink to fit into smaller spaces. This article explains all the fundamentals.
# Grid
CSS Grid Layout is the most powerful layout system available in CSS. It is a 2-dimensional system, meaning it can handle both columns and rows, unlike flexbox which is largely a 1-dimensional system. You work with Grid Layout by applying CSS rules both to a parent element (which becomes the Grid Container) and to that element's children (which become Grid Items).
# Document Object Model (DOM)
HTML as a document tree. Each tag is a node