Processes tree node.

@param {node} ast
function(ast) {
    let value = this.value;

    ast.traverse(function(node) {
      // If found block node stop at the next one for space check
      if (!node.is('block') && !node.is('atrulers')) return;

      if (node.first() &&
          node.first().is('space')) {
        node.first().content = value;
      } else if (value !== '') {
        var space = gonzales.createNode({
          type: 'space',
          content: value
        });
        node.insert(0, space);
      }
    });
  }