Principle Three – Understandable. Does the Reader Know How to Use an Ebook and Understand What They are Reading?
Written by
Monika Zarczuk-Engelsma
Posted on
Apr 9, 2026
Category
Accessibility
In the previous two articles, we looked at whether readers can access and use content at all. Now it's time for the third accessibility principle: understandable.
This principle answers two very important questions:
Does the user understand the content they are reading?
Do they really understand how to use the book?
Because even the most technically well-prepared ebook can be difficult if it is unreadable, unpredictable, or written in a way that makes it difficult to read.
Understandable Means More Than “Simple Language”
When we say “understandable”, the first thing that comes to mind is language. We consider whether the text is difficult, simple, or not overly specialized.
But, when it comes to accessibility, “understandable” means more than that.
It also depends on whether:
the book behaves predictably,
the reader knows what will happen after a given action,
the elements are described clearly,
the structure helps understand the content rather than complicating it.
Summing up: understandable is a principle that applies not only to what we write, but also to how we guide the reader through the book.
When the Reader Starts to Get Lost
Imagine a situation where a reader encounters a link but doesn't know where it leads.
They move on – the navigation suddenly changes.
They return – elements of the ebook work differently than before.
Another example:
a table appears without a caption, abbreviations without explanation, specialized terms without additional explanation or context.
At such moments, every reader stops focusing on the content. They begin to wonder what's actually going on.
Comprehensibility either dramatically decreases or completely disappears.
Consistency Gives You a Sense of Control
One of the key elements of an ebook being understandable is coherence.
If headings are constructed differently, their levelling is disrupted, for example, a heading appears in row 1, then row 2, then row 4,
if links are sometimes descriptive and sometimes not,
if elements work differently in different parts of the book,
the reader has to relearn the book each time, and this means effort.
A well-prepared ebook works predictably, the reader knows what to expect and doesn't have to guess how something works.
Words Matter
Understandable is also a matter of language, the way we describe things, give instructions, and provide guidance.
A link called "click here" says nothing, a link called "go to the accessibility chapter" says exactly what it needs to say.
The same applies to descriptions of elements, buttons, tables, photos, and references in the text - the more specific and contextualized they are, the easier it is to navigate them.
The sentence "more information below" doesn't say much.
The sentence "more information in the "Functionality" chapter" provides a specific point of reference.
If a table has no headers, the screen reader reads subsequent cells, but the reader does not know what the data refers to.
When it comes to photos and graphics, alt text plays a key role. If it's too generic, it doesn't help the reader. "Photo" in the alt text adds nothing.
"book cover with the title and author's name visible" – this makes it understandable why this element appears.
Even buttons and interactive elements matter.
"More" isn't enough.
"Show footnotes" or "Expand definition" clearly state what will happen after use.
These small editorial decisions make a huge difference.
A Difficult Text and a Specialised One Are Not the Same Thing
Publishers often worry that accessibility means simplifying the content. In practice, it's something else. A text can be specialized and yet understandable.
The difference lies in whether:
new concepts are introduced in context,
abbreviations are explained,
sentences are not unnecessarily complicated,
structure helps you follow the train of thought.
An example
A difficult, though specialized, fragment:
“The implementation of digital accessibility standards in electronic publications should take into account the WCAG guidelines, in particular in terms of perception, operability, understandability and compatibility, which allows for the optimization of the end-user experience.”
The same fragment, still specialized but understandable:
"When implementing accessibility in e-books, it's worth using the WCAG guidelines. They are based on four principles:
the content must be perceivable,
the book must be operable
must be understandable,
and work on different devices (be robust).
This allows the reader to truly benefit from the book – regardless of how they read it.”
So, contrary to popular belief, comprehensibility is not really about “simplifying the book,” it is about ensuring that the reader doesn’t have to guess what the author meant.
When the Form Complicates the Content
Sometimes the problem isn't the text itself, but the way it's presented.
Long, undivided paragraphs, a lack of clear sections, and headings that convey little.
In such cases, even a good text becomes difficult to read.
Structure, division of content and logical reader guidance are elements that can make content understandable for all recipients.
How Publishers Benefit from Creating Understandable Products
Comprehensibility very quickly translates into the quality of the book's reception.
This is the difference between a publication that is "readable" and one that you really understand and want to return to, that you will use for work, during a lecture, or that you will recommend to friends.
A well-prepared ebook prepared in keeping with all accessibility principles:
is more user-friendly for every reader,
builds trust in the publisher, to whom users are more willing to return,
reduces the reader’s frustration and fatigue,
works better in education and working with text.
Yes. It also means greater accessibility for people who read at a different pace, learn more slowly, have trouble absorbing complex content, or use translations or assistive technologies like screen readers.
“Understandable” Starts with Decisions
As with the previous principles, everything starts earlier than you might think.
Do we explain concepts?
Do we ensure coherence?
Do we describe elements clearly?
Do we guide the reader through the text?
Accessibility isn't about a book being merely "correct." This isn't enough for accessibility. It also means adhering to the third principle: making the book truly understandable.
In the next article, we'll look at fourth and last accessibility principle in the series: robust, or whether an e-book works properly with various devices and assistive technologies. We invite you to read it.
Bibliography:
https://dostepnapolska.pl/artykul/wcag-2025-zmiany-w-dostepnosci-cyfrowej-coraz-blizej
https://sensetec.pl/blog/standard-wcag-2-1/
https://wiedza.okno.pw.edu.pl/pl/materialy/rozszerzona_dostepnosc
https://digital-strategy.ec.europa.eu/pl/policies/web-accessibility-directive-standards-and-harmonisation[nh1]
https://www.w3.org/WAI/WCAG21/Understanding/intro?utm_source=chatgpt.com
https://appt.org/en/guidelines/wcag/principle-3?utm_source=chatgpt.com