vendors/tempy.js/push
    var parse = (input, options = {}) => {
      if (typeof input !== "string") {
        throw new TypeError("Expected a string");
      }
      let opts = options || {};
      let max = typeof opts.maxLength === "number" ? Math.min(MAX_LENGTH, opts.maxLength) : MAX_LENGTH;
      if (input.length > max) {
        throw new SyntaxError(`Input length (${input.length}), exceeds max characters (${max})`);
      }
      let ast = { type: "root", input, nodes: [] };
      let stack = [ast];
      let block = ast;
      let prev = ast;
      let brackets = 0;
      let length = input.length;
      let index = 0;
      let depth = 0;
      let value;
      let memo = {};
      const advance = () => input[index++];
      const push = (node) => {
        if (node.type === "text" && prev.type === "dot") {
          prev.type = "text";
        }
        if (prev && prev.type === "text" && node.type === "text") {
          prev.value += node.value;
          return;
        }
        block.nodes.push(node);
        node.parent = block;
        node.prev = prev;
        prev = node;
        return node;
      };
      push({ type: "bos" });
      while (index < length) {
        block = stack[stack.length - 1];
        value = advance();
        if (value === CHAR_ZERO_WIDTH_NOBREAK_SPACE || value === CHAR_NO_BREAK_SPACE) {
          continue;
        }
        if (value === CHAR_BACKSLASH) {
          push({ type: "text", value: (options.keepEscaping ? value : "") + advance() });
          continue;
        }
        if (value === CHAR_RIGHT_SQUARE_BRACKET) {
          push({ type: "text", value: "\\" + value });
          continue;
        }
        if (value === CHAR_LEFT_SQUARE_BRACKET) {
          brackets++;
          let closed = true;
          let next;
          while (index < length && (next = advance())) {
            value += next;
            if (next === CHAR_LEFT_SQUARE_BRACKET) {
              brackets++;
              continue;
            }
            if (next === CHAR_BACKSLASH) {
              value += advance();
              continue;
            }
            if (next === CHAR_RIGHT_SQUARE_BRACKET) {
              brackets--;
              if (brackets === 0) {
                break;
              }
            }
          }
          push({ type: "text", value });
          continue;
        }
        if (value === CHAR_LEFT_PARENTHESES) {
          block = push({ type: "paren", nodes: [] });
          stack.push(block);
          push({ type: "text", value });
          continue;
        }
        if (value === CHAR_RIGHT_PARENTHESES) {
          if (block.type !== "paren") {
            push({ type: "text", value });
            continue;
          }
          block = stack.pop();
          push({ type: "text", value });
          block = stack[stack.length - 1];
          continue;
        }
        if (value === CHAR_DOUBLE_QUOTE || value === CHAR_SINGLE_QUOTE || value === CHAR_BACKTICK) {
          let open = value;
          let next;
          if (options.keepQuotes !== true) {
            value = "";
          }
          while (index < length && (next = advance())) {
            if (next === CHAR_BACKSLASH) {
              value += next + advance();
              continue;
            }
            if (next === open) {
              if (options.keepQuotes === true)
                value += next;
              break;
            }
            value += next;
          }
          push({ type: "text", value });
          continue;
        }
        if (value === CHAR_LEFT_CURLY_BRACE) {
          depth++;
          let dollar = prev.value && prev.value.slice(-1) === "$" || block.dollar === true;
          let brace = {
            type: "brace",
            open: true,
            close: false,
            dollar,
            depth,
            commas: 0,
            ranges: 0,
            nodes: []
          };
          block = push(brace);
          stack.push(block);
          push({ type: "open", value });
          continue;
        }
        if (value === CHAR_RIGHT_CURLY_BRACE) {
          if (block.type !== "brace") {
            push({ type: "text", value });
            continue;
          }
          let type = "close";
          block = stack.pop();
          block.close = true;
          push({ type, value });
          depth--;
          block = stack[stack.length - 1];
          continue;
        }
        if (value === CHAR_COMMA && depth > 0) {
          if (block.ranges > 0) {
            block.ranges = 0;
            let open = block.nodes.shift();
            block.nodes = [open, { type: "text", value: stringify(block) }];
          }
          push({ type: "comma", value });
          block.commas++;
          continue;
        }
        if (value === CHAR_DOT && depth > 0 && block.commas === 0) {
          let siblings = block.nodes;
          if (depth === 0 || siblings.length === 0) {
            push({ type: "text", value });
            continue;
          }
          if (prev.type === "dot") {
            block.range = [];
            prev.value += value;
            prev.type = "range";
            if (block.nodes.length !== 3 && block.nodes.length !== 5) {
              block.invalid = true;
              block.ranges = 0;
              prev.type = "text";
              continue;
            }
            block.ranges++;
            block.args = [];
            continue;
          }
          if (prev.type === "range") {
            siblings.pop();
            let before = siblings[siblings.length - 1];
            before.value += prev.value + value;
            prev = before;
            block.ranges--;
            continue;
          }
          push({ type: "dot", value });
          continue;
        }
        push({ type: "text", value });
      }
      do {
        block = stack.pop();
        if (block.type !== "root") {
          block.nodes.forEach((node) => {
            if (!node.nodes) {
              if (node.type === "open")
                node.isOpen = true;
              if (node.type === "close")
                node.isClose = true;
              if (!node.nodes)
                node.type = "text";
              node.invalid = true;
            }
          });
          let parent = stack[stack.length - 1];
          let index2 = parent.nodes.indexOf(block);
          parent.nodes.splice(index2, 1, ...block.nodes);
        }
      } while (stack.length > 0);
      push({ type: "eos" });
      return ast;
    };