Meaningful Sequence
When the sequence in which content is presented affects its meaning, a correct reading sequence can be programmatically determined.
In plain language
If the order content is read in matters for understanding it, that reading order needs to be correct in the code — not just correct visually.
Why it matters
Screen readers read content in the order it appears in the code, not the order it looks on screen. If CSS is used to visually rearrange things without updating the code order, screen reader users hear content in a confusing, meaningless sequence.
In practice
Fails this criterion
A page uses CSS to visually reorder a multi-column layout, but the underlying HTML order doesn't match — a screen reader reads paragraphs in a jumbled sequence that doesn't make sense.
Meets this criterion
The HTML follows the same logical order as the visual reading order (top to bottom, column by column), so a screen reader reads content in the sequence it was meant to be understood.
Test it yourself
Use a screen reader (or disable CSS on the page) and go through the content. Does it still make sense in the order it's read out?