Detects the value of an option at the tree node.

@param {node} ast
function(ast) {
    let detected = [];

    ast.traverse(function(node, index, parent) {
      // If we see a zero with unit and it is not degree,
      // then we don’t have an option
      if (node.is('percentage') &&
          node.first('number').content[1] === '0') {
        detected.push(false);
        return;
      }

      if (node.is('dimension') &&
          node.first('number').content === '0' &&
          node.first('ident').content !== 'deg') {
        detected.push(false);
        return;
      }

      // If we see a zero and previous node is not percentage
      // or dimension, then we have an option
      if (node.is('number') &&
          node.content === '0' &&
          !parent.is('percentage') &&
          !parent.is('dimension')) {
        detected.push(true);
      }
    });

    return detected;
  }