为什么$pri用的是父类的属性?
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Group a series of buttons together on a single line with the button group, and super-power them with JavaScript.
<div class="btn-group" role="group" aria-label="Basic example">
<button type="button" class="btn btn-secondary">Left</button>
<button type="button" class="btn btn-secondary">Middle</button>
<button type="button" class="btn btn-secondary">Right</button>
</div>