KNOWLEDGE LIBRARY / CONCEPTS
Understand the why.
Put access into practice.
Accessibility makes more sense when you can see how it works. Explore the principles behind clear, usable websites and documents.
Start with what you’re making. Each card shows where a concept applies, an example, a common mistake, and a way to check your work.
Same principle, different tools. Format tags show where a concept is useful, not that every application works the same way. The explanations distinguish recommended practices from requirements and link to supporting guidance.
Explore the concepts
37 concepts
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Headings & structure
The main heading: the h1 rule
Give each webpage a clear main heading that identifies its purpose.
Applies to
Explore this concept: The main heading: the h1 rule
- Why it matters
- A recognizable starting point helps people orient themselves.
- Put it into practice
- One descriptive h1 is a useful convention for a typical page. Multiple h1 elements are not automatically a WCAG failure; evaluate the actual structure.
- An everyday example
- A registration page begins with “Register for the community workshop.”
- A common mistake
- Making the logo the only h1 on every page.
- How to check
- Inspect the heading list: does the main heading identify this specific page?
<h1>Register for the community workshop</h1>
Further reading
Headings & structure
Heading hierarchy and incrementation
Use heading levels to express which sections contain other sections.
Applies to
Explore this concept: Heading hierarchy and incrementation
- Why it matters
- A sensible outline makes long content easier to navigate.
- Put it into practice
- Use h2 for major sections below h1 and h3 for their subsections. Avoid skipping levels when opening a subsection. Returning from h3 to h2 starts a sibling section.
- An everyday example
- “Workshop details” is h2; “Location” is h3 within it. “Registration” can then be h2.
- A common mistake
- Choosing h4 because its default size looks right.
- How to check
- Read the outline without the body text. In Word, use heading styles; in PDF, inspect heading tags.
<h1>Community workshop</h1> <h2>Workshop details</h2> <h3>Location</h3> <h2>Registration</h2>
Further reading
Headings & structure
Heading level versus appearance
A large or bold paragraph is not necessarily a heading.
Applies to
Explore this concept: Heading level versus appearance
- Why it matters
- Visual formatting alone may not expose document structure.
- Put it into practice
- Assign the appropriate heading element, Word style, or PDF tag. Adjust its visual design separately.
- An everyday example
- Apply Heading 2 to “How to apply,” then change the style to match your brand.
- A common mistake
- Using bold text and extra blank lines instead of a real heading.
- How to check
- Check the navigation pane, heading list, or tag tree rather than judging by size.
Further reading
Headings & structure
Headings that describe their sections
A heading should help someone predict what comes next.
Applies to
Explore this concept: Headings that describe their sections
- Why it matters
- Readers often scan or jump between headings.
- Put it into practice
- Use specific labels that remain meaningful out of context.
- An everyday example
- “Request an accommodation” is clearer than “More information.”
- A common mistake
- Repeating “Details” for unrelated sections.
- How to check
- Read only the headings and ask whether they reveal the document’s organization.
Further reading
Navigation & interaction
Meaningful link text
Name the destination or purpose of a link.
Applies to
Explore this concept: Meaningful link text
- Why it matters
- A list of “click here” links offers little orientation.
- Put it into practice
- Use descriptive wording. Mention a download’s format when it helps the reader choose.
- An everyday example
- Use “Download the workshop checklist (PDF)” instead of “Click here.”
- A common mistake
- Using the same wording for different destinations.
- How to check
- Review links out of context and confirm that their destinations match their names.
Further reading
Navigation & interaction
A link takes you somewhere; a button performs an action.
Applies to
Explore this concept: Links versus buttons
- Why it matters
- People expect different keyboard behavior from each control.
- Put it into practice
- Use native HTML links for destinations and buttons for actions such as opening a dialog or filtering results.
- An everyday example
- “Read the guide” links to a page. “Clear filters” is a button.
- A common mistake
- Making a clickable div look like a button without its behavior.
- How to check
- Check the exposed role and test activation with the keyboard.
<a href="guide.html">Read the guide</a> <button type="button">Clear filters</button>
Further reading
Navigation & interaction
Reading order and focus order
The sequence should make sense beyond the visual layout.
Applies to
Explore this concept: Reading order and focus order
- Why it matters
- A two-column design can become confusing if content is read in the wrong order.
- Put it into practice
- Review reading sequence and interactive focus sequence separately. Visual placement does not guarantee either.
- An everyday example
- Read the event description before its registration instructions, then reach the registration link.
- A common mistake
- Moving content visually while leaving a confusing underlying order.
- How to check
- Navigate the document structure and Tab through controls. Check PDF tags and slide object order where relevant.
Further reading
Navigation & interaction
Keyboard access
People must be able to operate controls without a mouse.
Applies to
Explore this concept: Keyboard access
- Why it matters
- Some people use a keyboard, switch, or another input method.
- Put it into practice
- Use the platform’s expected keys. Tab moves between many controls; arrows move within grids and other widgets.
- An everyday example
- Open a menu, choose an item, and close it without clicking.
- A common mistake
- Checking only that Tab reaches the first control.
- How to check
- Complete a representative task, including any dialogs and exit routes, using the keyboard.
Further reading
Navigation & interaction
Visible keyboard focus
Make it clear which control is receiving keyboard input.
Applies to
Explore this concept: Visible keyboard focus
- Why it matters
- Without a visible indicator, a sighted keyboard user can lose their place.
- Put it into practice
- Preserve a clear focus indicator and check that overlays do not hide it.
- An everyday example
- A distinct outline follows the active link or button.
- A common mistake
- Removing outlines because they do not match the design.
- How to check
- Navigate controls on light and dark backgrounds and confirm you can always locate focus.
Further reading
Content & communication
Color and contrast
Keep content readable and communicate meaning through more than color.
Applies to
Explore this concept: Color and contrast
- Why it matters
- People perceive color and contrast differently.
- Put it into practice
- Check foreground/background contrast and pair color cues with words, symbols, or patterns.
- An everyday example
- Label an overdue invoice “Overdue” rather than relying on a red cell fill.
- A common mistake
- Assuming a dark-looking color always has enough contrast.
- How to check
- Measure relevant color pairs and inspect hover, focus, error, and selected states.
Further reading
Content & communication
Alternative text in context
Describe an image’s useful meaning or function, not every visible detail.
Applies to
Explore this concept: Alternative text in context
- Why it matters
- Important visual information needs another way to reach the reader.
- Put it into practice
- Use the format’s alternative-text feature. Treat decorative images appropriately and give complex information a fuller explanation.
- An everyday example
- For a chart, explain its main message and provide the supporting data nearby.
- A common mistake
- Accepting an automatic description without reviewing it.
- How to check
- Ask what information or action would be lost without the image.
Further reading
Navigation & interaction
Labels and instructions
Tell people what an input is for and what it expects.
Applies to
Explore this concept: Labels and instructions
- Why it matters
- An empty field should not become a guessing game.
- Put it into practice
- Provide a persistent label, associate it programmatically where supported, and explain required formats before entry.
- An everyday example
- “Date of birth (MM/DD/YYYY)” appears beside the input.
- A common mistake
- Using placeholder text as the only label.
- How to check
- Check the visible label and accessible name. For spreadsheet inputs, review surrounding labels and instructions.
Further reading
Navigation & interaction
Helpful error messages
Identify the problem and explain how to correct it.
Applies to
Explore this concept: Helpful error messages
- Why it matters
- Vague errors can stop a person from completing a task.
- Put it into practice
- Use text rather than color alone, preserve valid input, and expose feedback through the platform’s accessibility features.
- An everyday example
- “Enter an email address such as name@example.com” gives a usable next step.
- A common mistake
- Displaying only “Invalid” or clearing the entire form.
- How to check
- Try a missing value and an incorrect value, then follow the correction instructions.
Further reading
Headings & structure
Semantic structure
Use elements and document features that express the content’s purpose.
Applies to
Explore this concept: Semantic structure
- Why it matters
- Structure helps software interpret and navigate content.
- Put it into practice
- Use actual headings, lists, links, and table headers rather than visual imitations.
- An everyday example
- Use a numbered list for ordered steps, not separate paragraphs beginning with typed numbers.
- A common mistake
- Assuming a neatly arranged page has usable structure.
- How to check
- Inspect the document’s structure with the tools appropriate to its format.
Further reading
Content & communication
Zoom and reflow
Enlarging content should not make information or controls disappear.
Applies to
Explore this concept: Zoom and reflow
- Why it matters
- Some people need larger text or a narrow reading area.
- Put it into practice
- Let text adapt where supported. PDF behavior depends on tagging, layout, and reader support; it differs from responsive HTML.
- An everyday example
- A webpage becomes one column as the viewing area narrows.
- A common mistake
- Fixing a text box’s height so enlarged text gets clipped.
- How to check
- Enlarge the finished content and check for missing text, overlap, and unnecessary two-direction scrolling.
Further reading
Content & communication
Plain language and cognitive accessibility
Make information easier to find, understand, and use.
Applies to
Explore this concept: Plain language and cognitive accessibility
- Why it matters
- Unnecessary complexity adds effort and can conceal the next step.
- Put it into practice
- Use familiar words, explain necessary technical terms, and divide long tasks into manageable parts.
- An everyday example
- “Send the form by Friday” communicates an action and deadline directly.
- A common mistake
- Simplifying wording so much that important meaning is lost.
- How to check
- Ask a reader to explain the task in their own words and identify confusing points.
Further reading
Headings & structure
A useful page or document title
Give the file or browser tab a name that identifies its contents.
Applies to
Explore this concept: A useful page or document title
- Why it matters
- People need to distinguish documents and return to the right tab.
- Put it into practice
- Set the page title or document title metadata, not just a visible heading.
- An everyday example
- “Workshop registration | Common Ground Accessibility” identifies the page and organization.
- A common mistake
- Leaving “Untitled” or an internal draft filename as the published title.
- How to check
- Inspect the browser tab and document properties in the finished version.
Further reading
Content & communication
Document language
Identify the content’s primary language in the document settings.
Applies to
Explore this concept: Document language
- Why it matters
- Language information can help assistive technology pronounce text appropriately.
- Put it into practice
- Set the main language and mark passages in another language where the format supports it.
- An everyday example
- An English webpage uses lang="en" on its html element.
- A common mistake
- Assuming the language of your editing software automatically sets the document language.
- How to check
- Inspect language metadata and review pronunciation with the relevant assistive technology.
<html lang="en">
Further reading
Headings & structure
Real lists
Use the built-in list feature for related items or ordered steps.
Applies to
Explore this concept: Real lists
- Why it matters
- List structure communicates grouping and sequence.
- Put it into practice
- Use bullets when order is not essential and numbering when sequence matters.
- An everyday example
- A registration checklist uses a bulleted list; installation instructions use numbered steps.
- A common mistake
- Typing bullet characters or numbers into unrelated paragraphs.
- How to check
- Check that the authoring tool or output structure recognizes the content as a list.
Further reading
Tables & data
Accessible data tables
Make row, column, and header relationships understandable.
Applies to
Explore this concept: Accessible data tables
- Why it matters
- A value such as “$40” needs context to mean anything.
- Put it into practice
- Use clear headers and the table features supported by the format. Spreadsheet headers and HTML header associations are implemented differently.
- An everyday example
- A fees table identifies both the service and the price column.
- A common mistake
- Relying on bold text alone to identify header cells.
- How to check
- Move through the table and confirm that each value’s meaning remains clear.
Further reading
Tables & data
Informational tables versus layout tables
A data table communicates relationships; a layout table positions content.
Applies to
Explore this concept: Informational tables versus layout tables
- Why it matters
- Unnecessary table structure can obscure the actual reading sequence.
- Put it into practice
- On websites, use CSS for layout. For legacy layout tables, do not add data-table headers; presentation semantics may be appropriate. In documents and slides, prefer native layout tools. Spreadsheets require their own cell-structure approach.
- An everyday example
- A bus timetable is data. A table used only to place a portrait beside a biography is layout.
- A common mistake
- Adding header cells to a visual layout simply because it uses a table.
- How to check
- Ask whether interpreting each cell depends on a row or column heading.
Further reading
Tables & data
Simple spreadsheet structure
Keep the data area predictable and navigable.
Applies to
Explore this concept: Simple spreadsheet structure
- Why it matters
- Merged cells and unexplained gaps can interrupt navigation.
- Put it into practice
- Use consistent columns, clear headers, and simple contiguous data tables. Avoid merged cells and blank separator rows inside the data.
- An everyday example
- Keep one record per row and put notes outside the table with a clear introduction.
- A common mistake
- Adding empty rows to create visual spacing within a dataset.
- How to check
- Navigate the data with the keyboard and confirm that headers and boundaries remain understandable.
Further reading
Tables & data
Meaningful sheet names
Name each worksheet for the information it contains.
Applies to
Explore this concept: Meaningful sheet names
- Why it matters
- A descriptive tab makes it easier to find the right part of a workbook.
- Put it into practice
- Use short, distinct names and keep their wording consistent with the worksheet’s title.
- An everyday example
- “Workshop attendance” and “Expense summary” are more useful than “Sheet1” and “Sheet2.”
- A common mistake
- Keeping unused blank sheets in the published workbook.
- How to check
- Review the tab list without opening each sheet. Can a reader predict what they will find?
Further reading
Tables & data
Start in cell A1: the A1 rule
Use A1 as a useful starting point for each worksheet.
Applies to
Explore this concept: Start in cell A1: the A1 rule
- Why it matters
- A reader needs orientation before exploring a grid of cells.
- Put it into practice
- Place a meaningful title or introduction in A1. For complex sheets, identify where important tables or instructions begin. This is recommended practice, not a universal WCAG cell-position rule.
- An everyday example
- A1: “Workshop attendance. Participant table begins at A4; totals are on the Summary sheet.”
- A common mistake
- Leaving A1 blank while the worksheet starts several rows or columns away.
- How to check
- Navigate to A1 and ask whether it explains this sheet. Apply the principle in both Excel and Google Sheets.
A1: Workshop attendance. Participant table begins at A4. A4: Participant name | Session | Attendance status
Further reading
Tables & data
Charts need explanations
Make the chart’s message and underlying information available beyond its picture.
Applies to
Explore this concept: Charts need explanations
- Why it matters
- A chart can contain relationships that a short image label cannot explain.
- Put it into practice
- Provide a meaningful title, a concise takeaway, and an accessible data table or equivalent detail when needed.
- An everyday example
- “Workshop registrations rose from 20 in April to 35 in May” accompanies the chart.
- A common mistake
- Using color alone to distinguish chart series.
- How to check
- Hide the chart image and check whether the essential findings and values are still available.
Further reading
Documents & slides
Unique slide titles
Give every slide a meaningful, distinguishable title.
Applies to
Explore this concept: Unique slide titles
- Why it matters
- Titles help people navigate a presentation without inspecting every slide.
- Put it into practice
- Use the title placeholder where available. If the design hides a title, verify that it remains available to assistive technology.
- An everyday example
- Use “Workshop attendance: May” rather than repeating “Results” across several slides.
- A common mistake
- Treating a picture-only slide as if it needs no identifying title.
- How to check
- Review the slide outline or slide list using the presentation’s accessibility tools.
Further reading
Documents & slides
Logical slide object order
Arrange slide objects in a sequence that preserves meaning.
Applies to
Explore this concept: Logical slide object order
- Why it matters
- The order objects were added may differ from the order someone should read them.
- Put it into practice
- Review object order in the presentation tool and verify the reading order again after PDF export.
- An everyday example
- Read the slide title, then its explanation, then the chart and supporting note.
- A common mistake
- Assuming that objects positioned at the top are always read first.
- How to check
- Inspect reading-order tools and test the final presentation or PDF.
Further reading
Content & communication
Real text versus pictures of text
Use actual text instead of screenshots when possible.
Applies to
Explore this concept: Real text versus pictures of text
- Why it matters
- Real text can be searched, selected, resized, and interpreted by software.
- Put it into practice
- Publish the information as text in the format’s native content area. When an image is necessary, provide an appropriate equivalent.
- An everyday example
- Type the event details into the page rather than posting only a flyer image.
- A common mistake
- Assuming text visible inside a screenshot is available as text to everyone.
- How to check
- Try selecting and searching the wording, then inspect its accessibility representation.
Further reading
Documents & slides
OCR is only the beginning
Text recognition does not finish PDF accessibility.
Applies to
Explore this concept: OCR is only the beginning
- Why it matters
- A scan can become searchable while remaining difficult to navigate.
- Put it into practice
- Review OCR accuracy, then address tags, headings, reading order, language, links, and image alternatives as needed.
- An everyday example
- Correct a misread application deadline before adding structure to the scanned form.
- A common mistake
- Treating a successful OCR operation as an accessibility pass.
- How to check
- Check the recognized words against the page and inspect the document’s structure separately.
Further reading
Documents & slides
PDF tags describe structure behind the visible page.
Applies to
Explore this concept: PDF tags and reading order
- Why it matters
- Tags help identify content such as headings, paragraphs, and tables.
- Put it into practice
- Review tag types, nesting, and logical sequence. The presence of tags alone does not establish accessibility.
- An everyday example
- A two-column newsletter reads one article coherently before moving to the next.
- A common mistake
- Accepting automatic tags without checking their meaning or order.
- How to check
- Inspect the tag tree and test navigation and reading in a suitable PDF reader.
Further reading
Documents & slides
Accessible export
Preserve accessibility when converting a source file to PDF.
Applies to
Explore this concept: Accessible export
- Why it matters
- A usable source document can lose structure during conversion.
- Put it into practice
- Use an export workflow that supports accessibility and inspect its options. Printing to PDF may discard important structure.
- An everyday example
- Export a structured Word document with tagging enabled, then review the resulting PDF.
- A common mistake
- Checking only the source file before distributing the PDF.
- How to check
- Inspect headings, tables, links, language, and reading order in the exported file.
Further reading
Content & communication
Audio and visual information need appropriate alternatives.
Applies to
Explore this concept: Captions, transcripts, and descriptions
- Why it matters
- People may be unable to hear, see, or play the media.
- Put it into practice
- Captions convey speech and meaningful sounds; transcripts provide text; descriptions convey important visual information. Choose what the media needs.
- An everyday example
- An interview has corrected captions and a transcript; a silent demonstration also needs its actions explained.
- A common mistake
- Assuming automatic captions are accurate or describe everything visible.
- How to check
- Review alternatives against the media. For embedded or linked media, test the actual playback route.
Further reading
Checking & judgment
Accessibility checkers have limits
A clean automated report is useful evidence, not a complete evaluation.
Applies to
Explore this concept: Accessibility checkers have limits
- Why it matters
- Software cannot judge every aspect of meaning and usability.
- Put it into practice
- Combine automated checks with manual review and relevant assistive-technology testing.
- An everyday example
- A checker notices missing alt text; a person evaluates whether the description fits the image’s purpose.
- A common mistake
- Equating zero reported errors with a fully accessible experience.
- How to check
- Review a real task and document what was checked, how, and what remains uncertain.
Further reading
Content & communication
Clear instructions and predictable layouts
Reduce the effort needed to find and remember the next step.
Applies to
Explore this concept: Clear instructions and predictable layouts
- Why it matters
- People should not have to reconstruct instructions from scattered clues.
- Put it into practice
- Keep related information together, explain unfamiliar actions, and present multi-step tasks in a sensible sequence.
- An everyday example
- Place upload limits beside the upload control before someone selects a file.
- A common mistake
- Revealing an important instruction only after the person makes an error.
- How to check
- Follow the task as a new reader and identify anything you had to infer or remember unnecessarily.
Further reading
Checking & judgment
Requirement, recommendation, or convention?
Explain the authority and scope behind an accessibility statement.
Applies to
Explore this concept: Requirement, recommendation, or convention?
- Why it matters
- Calling every useful practice a mandatory rule can mislead people.
- Put it into practice
- Distinguish standards requirements from implementation techniques, organizational policies, and helpful conventions. State the version and context when citing a requirement.
- An everyday example
- A1 orientation is a useful spreadsheet practice; WCAG does not name a universal required starting cell.
- A common mistake
- Presenting a preferred design pattern as the only conforming implementation.
- How to check
- Follow the source link and identify whether it states a requirement or offers guidance.
Further reading
Checking & judgment
Accessibility versus appearance
A polished appearance does not establish usable structure or behavior.
Applies to
Explore this concept: Accessibility versus appearance
- Why it matters
- Visual review shows only part of the experience.
- Put it into practice
- Inspect what the format exposes to software as well as what appears on the screen.
- An everyday example
- A beautiful schedule can still be confusing if row labels are not associated with its values.
- A common mistake
- Assuming clean spacing and consistent colors mean a file is accessible.
- How to check
- Pair a visual review with structural checks and representative navigation tasks.
Further reading
Checking & judgment
Test the finished version
Review the version people will actually receive and use.
Applies to
Explore this concept: Test the finished version
- Why it matters
- Publishing and conversion can introduce new barriers.
- Put it into practice
- Check the live URL, shared workbook, presentation, or exported PDF after the final changes.
- An everyday example
- Follow a download link from the live page and test the downloaded file, not only your local draft.
- A common mistake
- Retaining an old accessibility report after changing the content.
- How to check
- Confirm links, reading sequence, keyboard access, and important content in the published version.
Further reading
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