Nothing
Code
actionButton("foo", "Click me")
Output
<button id="foo" type="button" class="btn btn-default action-button">
<span class="action-label">Click me</span>
</button>
Code
actionButton("foo", "Click me", icon = icon("star"))
Output
<button id="foo" type="button" class="btn btn-default action-button">
<span class="action-icon">
<i class="far fa-star" role="presentation" aria-label="star icon"></i>
</span>
<span class="action-label">Click me</span>
</button>
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