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Best Practice
Best practice is to try and provide descriptive link /text or button labels by default.
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The speech to input user will not know what the aria-label is as it is not visible to them. However if the aria-label starts out with the default button label, "Learn more about London Breed", the speech recognition software will be able to recognize that button label.
Ensure that Links Appear in Context
Provide links at the point in the content at which they're useful without visibly displaying the URL or "here".