In the previous lessons we saw that almost every accessibility law in the world refers to the same technical standard: WCAG. The time has come to open it up and understand how it is built inside. In this lesson you will learn what WCAG is and who publishes it, its hierarchical structure (the 4 POUR principles → guidelines → success criteria → techniques), the three conformance levels A / AA / AAA and why AA is the usual target, the differences between versions 2.0, 2.1, and 2.2 (and what WCAG 3.0 will be), and how to read the nomenclature of a criterion like the famous "1.1.1." With this, we close the introductory module: you will have the complete mental map to dive into the details starting in the next module.

1. What WCAG is and who publishes it
2. The hierarchical structure: principles → guidelines → criteria → techniques
3. The conformance levels A, AA, and AAA
4. WCAG versions: 2.0, 2.1, 2.2, and the future 3.0
5. How to read a success criterion (the 1.1.1 nomenclature)

WCAG stands for Web Content Accessibility Guidelines. It is the international standard that defines, concretely and verifiably, what web content must meet in order to be accessible.

It is published by the W3C (World Wide Web Consortium), the body that standardizes the web, through its WAI (Web Accessibility Initiative). The fact that it is a W3C standard—and not one from a single vendor—is what gives it universal authority and explains why laws adopt it as a reference (we saw this in lesson 01-03).

The central idea of WCAG is to turn an abstract concept ("being accessible") into a list of checkable requirements (the success criteria). This way, accessibility stops being an opinion and becomes something that can be audited: either you meet a criterion or you don't.

WCAG is organized as a four-level tree. Understanding this hierarchy is the most important part of the lesson, because it is the "skeleton" on which everything else hangs.

Level by level:

• Principles (4). They are the foundations, summed up in the acronym POUR: Perceivable, Operable, Understandable, and Robust. Every criterion belongs to one of them. In this lesson we use them only as a structural framework; they are developed in depth in Module 3.
• Guidelines. Under each principle there are guidelines: general goals, not verifiable on their own. Example: under Perceivable is guideline 1.1 "Text alternatives."
• Success Criteria. This is the practical heart of WCAG: concrete, checkable requirements, each with a level (A, AA, or AAA). When someone says "the site meets WCAG AA," they mean that it satisfies all level A and AA criteria. Example: criterion 1.1.1 "Non-text content."
• Techniques. They are advisory examples of how to meet a criterion (using alt, applying an ARIA role, etc.). They are not mandatory: you can meet a criterion with a different technique. They are implementation advice, and we will see them applied in Modules 4 and 5.

A key nuance for beginners: what you audit and what the law requires are the criteria, not the techniques. Techniques tell you "one way to achieve it"; the criterion tells you "what has to be achieved."

Each success criterion is labeled with one of three levels, which express how demanding and essential it is. They are cumulative: AA includes all of A, and AAA includes all of A and AA.

For two reasons that you have already seen surface in lesson 01-03:

1. It is what the law requires. Practically every regulation (EN 301 549, EAA, RD 1112/2018, Section 508…) asks for level AA.
2. It is the sensible balance. Level A leaves too many people out; AAA is so strict that the W3C itself acknowledges that "it is not recommended to require it as a general policy for entire sites" (some AAA criteria are incompatible with certain types of content). AA is the point at which the vast majority of barriers are removed with a manageable effort.

For Cursalia, therefore, the goal we will set throughout the course is WCAG 2.1 level AA, occasionally aspiring to AAA criteria where it is easy and adds value (for example, more than the minimum contrast in the brand palette).

WCAG has evolved over time. The reassuring part is that the 2.x versions are backward-compatible: each new version adds criteria, it does not remove the previous ones. If you meet 2.2, you meet 2.1 and 2.0.

As a practical reference: today, aim for WCAG 2.1 AA (what current laws ask for) and, if you can, incorporate the new items from 2.2. WCAG 3.0 is the future and should not yet be used as a compliance target; we will talk about it and other trends in Module 7.

Criteria are identified by three numbers separated by dots, and that code is a "GPS" within the hierarchy. Let's take the most famous one, 1.1.1 "Non-text content":

That is:

• The first number is the principle: 1 = Perceivable, 2 = Operable, 3 = Understandable, 4 = Robust.
• The second number is the guideline within that principle (1.1 = "Text alternatives").
• The third number is the specific criterion within that guideline.
• Separately, each criterion carries its level (A / AA / AAA).

Here are some examples you will run into again and again throughout the course, so the nomenclature becomes familiar:

Just by looking at the number, you already know which "family" a requirement belongs to. For example, when in Module 4 we audit Cursalia's enrollment form and talk about criterion 3.3.2, the "3" will tell you instantly that it is a matter of understanding (clear labels and instructions), not of perception or robustness.

• Confusing criteria with techniques. What is mandatory and auditable are the criteria; techniques are only one way to meet them. You are not tied to a specific technique.
• Aspiring to AAA for the whole site. It is usually unattainable and hardly any law asks for it. The target is AA; use AAA selectively and voluntarily.
• Thinking that versions replace one another. They don't: 2.1 and 2.2 add criteria on top of 2.0. Meeting the newest one implies meeting the earlier ones.
• Using WCAG 3.0 as a target today. It is still a draft; it can't be used to declare conformance.
• Tip: memorize that the first digit of the criterion = POUR principle (1-P, 2-O, 3-U, 4-R). It is the fastest way to orient yourself when reading an accessibility report (which you will learn to interpret in Module 6).

Exercise 1. Order these four WCAG elements from highest to lowest in the hierarchy and define each in one sentence: success criterion, principle, technique, guideline.

Exercise 2. Given criterion 2.1.1 "Keyboard" (Level A), answer: (a) which POUR principle does it belong to? (b) what does its level A mean? (c) why do you think the requirement "everything works with a keyboard" is level A and not AAA?

Exercise 3. The Cursalia team says: "We're going to certify the whole platform in WCAG 3.0 AAA to be on the safe side." Point out two problems with that statement.

Solution 1. From highest to lowest: Principle (one of the 4 POUR foundations) → Guideline (a general, non-verifiable goal within a principle) → Success criterion (a concrete, checkable requirement, with level A/AA/AAA) → Technique (an advisory, non-mandatory way to meet a criterion).

Solution 2. (a) It belongs to principle 2 · Operable (indicated by the first digit). (b) Level A = an essential minimum requirement; without it, there are users who simply cannot use the content. (c) Because someone who can't use the mouse (due to a motor disability) would be completely excluded if something only works with a click: it is a total barrier, not a refinement, and that is why it sits at the most basic level (A).

Solution 3. Two problems: (1) WCAG 3.0 is still a draft and cannot be used to declare conformance; the current reference is WCAG 2.1 (or 2.2) AA. (2) Level AAA is not recommended as a target for an entire site (the W3C itself advises against it) and is usually unattainable; what is required and sensible is AA.

We have opened up WCAG and understood its anatomy: it is the W3C/WAI standard that turns "being accessible" into verifiable criteria, organized in a hierarchy of 4 POUR principles → guidelines → criteria → techniques. We know there are three levels (A, AA, AAA) and why AA is the usual target—the one we set for Cursalia—we distinguish the 2.0/2.1/2.2 versions (with 3.0 on the horizon), and we now know how to read the nomenclature of a criterion like 1.1.1, whose first digit reveals which principle it belongs to.

With this, we close Module 1: Introduction to Web Accessibility. You now have the complete map: what accessibility is, why it matters, which laws require it, and how the standard that underpins them is structured. However, to apply WCAG well, an essential prior step is needed: understanding the people we design for. In Module 2: Understanding Disabilities and Assistive Technologies we will get to know the types of disability, the assistive technologies (such as screen readers), and how people with disabilities actually use the web. That knowledge will give meaning and purpose to every technical criterion we implement afterward.