Otherwise, NIL is returned.

See <a href="#CONDITION%20CLIP%3AUNKNOWN-ATTRIBUTE" class="xref">UNKNOWN-ATTRIBUTE</a></pre></div> </article> </li>  <li> <article class="definition function callable" id="FUNCTION CLIP:CHECK-SOLE-ATTRIBUTE"> <header> <span class="visibility">EXTERNAL</span> <span class="type">FUNCTION</span> <h4 class="name"> <a href="#FUNCTION%20CLIP%3ACHECK-SOLE-ATTRIBUTE">CHECK-SOLE-ATTRIBUTE</a> </h4> <ul class="qualifiers"></ul> <ul class="arguments">  <li class="argument">NODE</li>    <li