relativeURLs to true is ignored outside href

Layout file contains something like following lines.

{{ $lib := "libs" | relURL }}
{{ $lib }}
<link rel="stylesheet" href="{{ "libs" | relURL }}">

Configuration contains relativeURLs = true.

When Hugo generates following output.

/libs
<link rel="stylesheet" href="../libs">

Path in first line must be equal to path on the second line, but not. Why?