Do not override author-set, global attributes

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Global attributes are those that are present on all HTML elements. Some examples include tabindex and role. A custom element may wish to set its initial tabindex to 0 so it will be keyboard focusable. But you should always check first to see if the developer using your element has set this to another value. If, for example, they've set tabindex to -1, it's a signal that they don't wish for the element to be interactive.

Ensure that there is a check for the attribute before altering (set/remove) the attribute in the connectedCallback.

if (!this.hasAttribute('foo')) this.setAttribute('foo', 'bar')

Resource:
https://developers.google.com/web/fundamentals/web-components/best-practices#do-not-override-author-set-global-attributes
https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes