Can I just make up attributes on my HTML tags?

<a href="something.html" hastooltip="yes" tipcolour="yellow">...</a>

<a href="..." class="class-one class-two has-tooltip">

<a href="..." class="has-tooltip common-tooltip">
<a href="..." class="has-tooltip long-tooltip">

a.has-tooltip {
   colour: red;
}
a.common-tooltip {
   background: #ddd;
}
a.long-tooltip {
   background: #ebf;
}