code: function(root) {
      var tables = root.getElementsByTagName("table");
      for (var i = 0; i < tables.length; i++) {
        var table = tables[i];
        var role = table.getAttribute("role");
        if (role == "presentation") {
          table._readabilityDataTable = false;
          continue;
        }
        var datatable = table.getAttribute("datatable");
        if (datatable == "0") {
          table._readabilityDataTable = false;
          continue;
        }
        var summary = table.getAttribute("summary");
        if (summary) {
          table._readabilityDataTable = true;
          continue;
        }
  
        var caption = table.getElementsByTagName("caption")[0];
        if (caption && caption.childNodes.length > 0) {
          table._readabilityDataTable = true;
          continue;
        }
  
        // If the table has a descendant with any of these tags, consider a data table:
        var dataTableDescendants = ["col", "colgroup", "tfoot", "thead", "th"];
        var descendantExists = function(tag) {
          return !!table.getElementsByTagName(tag)[0];
        };
        if (dataTableDescendants.some(descendantExists)) {
          this.log("Data table because found data-y descendant");
          table._readabilityDataTable = true;
          continue;
        }
  
        // Nested tables indicate a layout table:
        if (table.getElementsByTagName("table")[0]) {
          table._readabilityDataTable = false;
          continue;
        }
  
        var sizeInfo = this._getRowAndColumnCount(table);
        if (sizeInfo.rows >= 10 || sizeInfo.columns > 4) {
          table._readabilityDataTable = true;
          continue;
        }
        // Now just go by size entirely:
        table._readabilityDataTable = sizeInfo.rows * sizeInfo.columns > 10;
      }
    }
docs: Look for 'data' (as opposed to 'layout') tables, for which we use
  similar checks as
  https://dxr.mozilla.org/mozilla-central/rev/71224049c0b52ab190564d3ea0eab089a159a4cf/accessible/html/HTMLTableAccessible.cpp#920