CS I · Wed Dec 2 · 17.3 · Do Now

Who Gets Left Out

Open the discussion form on the right and answer Section 1 from your first reading.

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Accessibility

This section explains how a builder checks whether a program leaves some people out. A program can work every time it runs and still not work for everyone who tries to use it. The AP Computer Science A course calls this the impact of a program, and it says the impacts can be beneficial or harmful. Every program helps some people, and a program built to fill a need can still leave other people out.

What Accessibility Means

Accessibility means building a program or page so that people with disabilities can use it. The W3C's Web Accessibility Initiative lists visual, hearing, physical, speech, cognitive and neurological disabilities. The same changes help many other people as well. For example, the W3C names a person using a screen in bright sunlight, a person with a broken arm, and older people whose abilities change with age. A page that works for its builder has not been checked for accessibility, because the builder is only one kind of user.

Contrast

Contrast is the difference in brightness between text and its background. It is measured as a ratio, which runs from 1 to 1, for no contrast at all, up to 21 to 1, for black text on a white background. The ratio is calculated from the two colors with a formula in the W3C's Web Content Accessibility Guidelines. The guidelines set a minimum of 4.5 to 1 for ordinary text, so that people with moderately low vision can read it, and large text has a lower minimum. For example, gray text in the color #999999 on a white background measures 2.85 to 1, which is below the minimum. A darker gray, #595959, measures 7.00 to 1 on white and meets the minimum. Figure 1 shows the same sentence printed in both grays.

Hue is not a key factor in the formula, so two colors that look different to one person can still have low contrast, and contrast is measured instead of judged by eye. The grays #777777 and #767676 look almost the same. On white, the first measures 4.48 to 1 and the second measures 4.54 to 1, so the two grays land on opposite sides of the line. The guidelines say that a ratio is not rounded up, so 4.48 to 1 does not meet the minimum.

The Bench Basics code panel was checked this way on October 20, 2026. Its code is dark ink, #1B1B1B, which measures 16.49 to 1 on the off-white panel, #FBFAF6, and 15.48 to 1 on the pale yellow highlight of the line being traced, #FFF3C4. Both pairs meet the minimum, but the line numbers did not. Their gray, #8A8576, measured 3.53 to 1 on the panel and 3.31 to 1 on the highlight. It was darkened to #66624F and measured again, at 5.87 to 1 and 5.51 to 1, so the line numbers now meet the minimum. White text on the copper Check buttons, #C2622F, measured 4.13 to 1, so the copper was darkened to #A04E1D, which measures 5.83 to 1.

Alt Text and the Keyboard

Alt text is a short written description of an image, stored in the page with the image. A screen reader is software that reads a page aloud for a person who cannot see it, and it reads the alt text in place of the image. Good alt text is brief, and it says what the image shows that the words around it do not. For example, Figure 1 shows a picture of a classroom with its alt text beside it, and the alt text names the students, their laptops and the whiteboard. A file name such as IMG_2041.png is not alt text, because it describes nothing about the image. The W3C lists a file name used in place of alt text as a failure, and some screen readers read the file name aloud when an image has no alt text.

A page should also work with the keyboard alone, because some people cannot use a mouse. On a web form, the Tab key moves from one control to the next.

Checking Is Part of Building

The AP course also notes that a program meant to fill a need can have harmful effects that its builder did not intend. A page that leaves out a person with low vision is one such effect, and checking for it is part of building a program. The bench's line numbers show how such a check works: a color is measured, found below the minimum, changed and measured again.

Summary

Accessibility means building a page so that people with disabilities can use it, and the same changes help many other people. Contrast is measured as a ratio from 1 to 1 up to 21 to 1, with a minimum of 4.5 to 1 for ordinary text, and alt text gives a screen reader words to read in place of an image.

Sources: W3C WAI, Introduction to Web Accessibility (2026); W3C WAI, Understanding SC 1.4.3: Contrast (Minimum) (2026); W3C WAI, Understanding SC 1.1.1: Non-text Content (2026); MDN Web Docs, What is accessibility? (2026); MDN Web Docs, HTML: A good basis for accessibility (2026); College Board, AP Computer Science A Course and Exam Description (2025); Bench Basics colors and contrast ratios, course site (2026).

I Do questions
  1. notebook cue: accessibility

    Name one person, other than a person who is blind, who is helped when a page is accessible.

    Check

    One answer is a person using a screen in bright sunlight. The W3C also names a person with a broken arm and older people whose abilities change with age, and a person with low vision is helped by good contrast. See What Accessibility Means, paragraph 1.

  2. notebook cue: contrast

    Figure 1 shows two gray-on-white pairs and their ratios. Which one meets the minimum for ordinary text, and how do you know?

    Check

    The darker gray, #595959, meets it. Its ratio is 7.00 to 1, which is above the minimum of 4.5 to 1, while #999999 measures only 2.85 to 1. See Contrast, paragraph 1, and Figure 1.

  3. notebook cue: alt text

    Write alt text for the picture of the classroom in Figure 1.

    Check

    One good answer is the alt text Figure 1 gives: "Three students at desks with open laptops face a whiteboard at the front of a classroom." Good alt text is brief and says what the picture shows, and a file name such as IMG_2041.png is not alt text. See Alt Text and the Keyboard, paragraph 1.

Figure 1. The same sentence in two grays on white, with each measured contrast ratio, and a picture of a classroom with the alt text that a screen reader reads aloud in its place.
I Do questions
  1. notebook cue: accessibility

    Name one person, other than a person who is blind, who is helped when a page is accessible.

    Check

    One answer is a person using a screen in bright sunlight. The W3C also names a person with a broken arm and older people whose abilities change with age, and a person with low vision is helped by good contrast. See What Accessibility Means, paragraph 1.

  2. notebook cue: contrast

    Figure 1 shows two gray-on-white pairs and their ratios. Which one meets the minimum for ordinary text, and how do you know?

    Check

    The darker gray, #595959, meets it. Its ratio is 7.00 to 1, which is above the minimum of 4.5 to 1, while #999999 measures only 2.85 to 1. See Contrast, paragraph 1, and Figure 1.

  3. notebook cue: alt text

    Write alt text for the picture of the classroom in Figure 1.

    Check

    One good answer is the alt text Figure 1 gives: "Three students at desks with open laptops face a whiteboard at the front of a classroom." Good alt text is brief and says what the picture shows, and a file name such as IMG_2041.png is not alt text. See Alt Text and the Keyboard, paragraph 1.

Accessibility

This section explains how a builder checks whether a program leaves some people out. A program can work every time it runs and still not work for everyone who tries to use it. The AP Computer Science A course calls this the impact of a program, and it says the impacts can be beneficial or harmful. Every program helps some people, and a program built to fill a need can still leave other people out.

What Accessibility Means

Accessibility means building a program or page so that people with disabilities can use it. The W3C's Web Accessibility Initiative lists visual, hearing, physical, speech, cognitive and neurological disabilities. The same changes help many other people as well. For example, the W3C names a person using a screen in bright sunlight, a person with a broken arm, and older people whose abilities change with age. A page that works for its builder has not been checked for accessibility, because the builder is only one kind of user.

Contrast

Contrast is the difference in brightness between text and its background. It is measured as a ratio, which runs from 1 to 1, for no contrast at all, up to 21 to 1, for black text on a white background. The ratio is calculated from the two colors with a formula in the W3C's Web Content Accessibility Guidelines. The guidelines set a minimum of 4.5 to 1 for ordinary text, so that people with moderately low vision can read it, and large text has a lower minimum. For example, gray text in the color #999999 on a white background measures 2.85 to 1, which is below the minimum. A darker gray, #595959, measures 7.00 to 1 on white and meets the minimum. Figure 1 shows the same sentence printed in both grays.

Hue is not a key factor in the formula, so two colors that look different to one person can still have low contrast, and contrast is measured instead of judged by eye. The grays #777777 and #767676 look almost the same. On white, the first measures 4.48 to 1 and the second measures 4.54 to 1, so the two grays land on opposite sides of the line. The guidelines say that a ratio is not rounded up, so 4.48 to 1 does not meet the minimum.

The Bench Basics code panel was checked this way on October 20, 2026. Its code is dark ink, #1B1B1B, which measures 16.49 to 1 on the off-white panel, #FBFAF6, and 15.48 to 1 on the pale yellow highlight of the line being traced, #FFF3C4. Both pairs meet the minimum, but the line numbers did not. Their gray, #8A8576, measured 3.53 to 1 on the panel and 3.31 to 1 on the highlight. It was darkened to #66624F and measured again, at 5.87 to 1 and 5.51 to 1, so the line numbers now meet the minimum. White text on the copper Check buttons, #C2622F, measured 4.13 to 1, so the copper was darkened to #A04E1D, which measures 5.83 to 1.

Alt Text and the Keyboard

Alt text is a short written description of an image, stored in the page with the image. A screen reader is software that reads a page aloud for a person who cannot see it, and it reads the alt text in place of the image. Good alt text is brief, and it says what the image shows that the words around it do not. For example, Figure 1 shows a picture of a classroom with its alt text beside it, and the alt text names the students, their laptops and the whiteboard. A file name such as IMG_2041.png is not alt text, because it describes nothing about the image. The W3C lists a file name used in place of alt text as a failure, and some screen readers read the file name aloud when an image has no alt text.

A page should also work with the keyboard alone, because some people cannot use a mouse. On a web form, the Tab key moves from one control to the next.

Checking Is Part of Building

The AP course also notes that a program meant to fill a need can have harmful effects that its builder did not intend. A page that leaves out a person with low vision is one such effect, and checking for it is part of building a program. The bench's line numbers show how such a check works: a color is measured, found below the minimum, changed and measured again.

Summary

Accessibility means building a page so that people with disabilities can use it, and the same changes help many other people. Contrast is measured as a ratio from 1 to 1 up to 21 to 1, with a minimum of 4.5 to 1 for ordinary text, and alt text gives a screen reader words to read in place of an image.

Sources: W3C WAI, Introduction to Web Accessibility (2026); W3C WAI, Understanding SC 1.4.3: Contrast (Minimum) (2026); W3C WAI, Understanding SC 1.1.1: Non-text Content (2026); MDN Web Docs, What is accessibility? (2026); MDN Web Docs, HTML: A good basis for accessibility (2026); College Board, AP Computer Science A Course and Exam Description (2025); Bench Basics colors and contrast ratios, course site (2026).

Table Talk
Think of a website or app you use. Name one person who might have trouble using it, and one thing on the screen that would cause the trouble.

Each table picks one app from its answers and agrees on the one change that would help the most people.

Chromebooks stay closed while your table talks. Sections 1 and 2 of the discussion form are already done. After you talk, finish Section 3 right here under My View. Submit before the exit ticket.

Open the discussion form

This form has three sections. Section 1: answer today's Board Question. Section 2: after the reading. Section 3 opens later in class. Today's Board Question: Think of a website or app you use. Name one person who might have trouble using it, and one thing on the screen that would cause the trouble.

CR 1. Board Question: Think of a website or app you use. Name one person who might have trouble using it, and one thing on the screen that would cause the trouble. Give your answer and one reason.

Write your answer in your lab notebook, labeled CR 1.

MC 1. Think about your answer to the board question. Think of a website or app you use. Name one person who might have trouble using it, and one thing on the screen that would cause the trouble. Which position is closest to yours now?

  • A person who cannot see well, because the text is small or faint.
  • A person who cannot use a mouse, because some buttons only work with a click.
  • Nobody. If it is on the web, everyone can use it.

MC 2. (Reading claim 1) Accessibility changes help only people with disabilities.

  • Agree
  • Disagree

MC 3. (Reading claim 2) A screen reader reads alt text aloud in place of an image.

  • Agree
  • Disagree

MC 4. (Reading claim 3) Contrast can be measured as a number.

  • Agree
  • Disagree

MC 5. (Reading claim 4) In Figure 1, the sentence printed in #595959 meets the minimum for ordinary text.

  • Agree
  • Disagree

MC 6. (Reading claim 5) Gray #777777 on white meets the minimum, because 4.48 to 1 rounds up to 4.5 to 1.

  • Agree
  • Disagree

MC 7. (Reading claim 6) A file name such as IMG_2041.png is good alt text, because it names the image.

  • Agree
  • Disagree

MC 8. (Reading claim 7) On Oct 20, the bench's line numbers measured below 4.5 to 1, so their gray was darkened until it met the minimum.

  • Agree
  • Disagree

MC 9. (Reading claim 8) In an if, else if and else chain, two branches can both run when two conditions are true.

  • Agree
  • Disagree

CR 2. (A different view) Write the view at your table that was most different from yours. If everyone agreed, write the strongest argument against your table's answer.

Write your answer in your lab notebook, labeled CR 2.

CR 3. Think about the Board Question again: Think of a website or app you use. Name one person who might have trouble using it, and one thing on the screen that would cause the trouble. Do you have the same opinion as when you first answered the board question? If it is the same, what from the reading or table talk reaffirmed your opinion? If it is different, what from the reading or table talk changed your opinion?

Write your answer in your lab notebook, labeled CR 3.