Question

In my HTML code I have a tag with a span tag inherited. My question is now how can I achieve that the text in the link-element will be underlined on hover and the span-element not?

HTML:

<a class="tooltip" href="#">
  Link, should be underlined on hover.
  <span class="custom info">Span, shouldn't be underlined on hover.</span>
</a>

CSS:

/* General settings */

a { color: black; text-decoration: none }
a:visited { color: black; }
a:hover { color: #1af; text-decoration: underline }

/* End */

.tooltip {
    position: relative;
}

.tooltip span {
    display:none;
    position: absolute;
    white-space:nowrap;
    border-radius: 5px 5px; -moz-border-radius: 5px; -webkit-border-radius: 5px;
    box-shadow: 5px 5px 5px rgba(0, 0, 0, 0.1); 
    -webkit-box-shadow: 5px 5px rgba(0, 0,0, 0.1); 
    -moz-box-shadow: 5px 5px rgba(0, 0, 0, 0.1);
    font-family: Calibri, Tahoma, Geneva, sans-serif;
    margin-left: 0; 
    z-index: 1;
    text-decoration: none;
}

a.tooltip:hover span {
    display:block;
    text-decoration: none;
}

Answer 1

You could add another span (AKA HTML’s inline duct tape) and move the :hover styling to that:

<a class="tooltip" href="#">
    <span class="hack">Link, should be underlined on hover.</span>
    <span class="custom info">Span, shouldn't be underlined on hover.</span>
</a>

And:

a:hover span.hack { color: #1af; text-decoration: underline }
/*...*/
.tooltip span.info {
    /*...*/
    /* Remove text-decoration */
}
a.tooltip:hover span {
    display:block;
}

Demo: http://jsfiddle.net/ambiguous/UWgcc/1/

You’d probably want to rename the hack class, I was just being honest with that.

If you only want to mess around with your .tooltip links, then you could add this to the above:

a:hover { color: #1af; text-decoration: underline }
a.tooltip:hover { color: #000; text-decoration: none }

Demo: http://jsfiddle.net/ambiguous/UWgcc/2/