What this snippet does
An unset variable interpolates to an empty string and the image reference becomes invalid.
Expected output
WARN: The "TAG" variable is not set. Defaulting to a blank string.
Why practise typing this
Typing compose advanced code builds muscle memory for the symbols and indentation Docker uses most, which prose-based typing tests never cover. DevType measures your words per minute and accuracy on this snippet and tracks the individual characters you mistype, so later lessons can target them.
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