diff --git a/src/bar.js b/src/bar.js
index 21bcf3a..a8d4cec 100644
--- a/src/bar.js
+++ b/src/bar.js
@@ -34,7 +34,7 @@ export default class Bar {
       this.duration *
       (this.task.progress / 100) || 0;
     this.group = createSVG("g", {
-      class: "bar-wrapper " + (this.task.custom_class || "") + (this.task.important && 'important'),
+      class: "bar-wrapper" + (this.task.custom_class ? " " + this.task.custom_class : "") + (this.task.important ? ' important' : ''),
       "data-id": this.task.id,
     });
     this.bar_group = createSVG("g", {
diff --git a/src/index.js b/src/index.js
index d2c2916..a1f1816 100644
--- a/src/index.js
+++ b/src/index.js
@@ -100,7 +100,8 @@ export default class Gantt {
       language: "en",
       readonly: false,
       highlight_weekend: true,
-      scroll_today: true
+      scroll_today: true,
+      lines: 'both'
     };
     this.options = Object.assign({}, default_options, options);
     if (!options.view_mode_padding) options.view_mode_padding = {}
@@ -132,12 +133,17 @@ export default class Gantt {
         });
       }
       task._end = date_utils.parse(task.end);
-
+      let diff = date_utils.diff(task._end, task._start, "year");
+      if (diff < 0) {
+        console.log(task._end, task._start)
+        throw Error("start of task can't be after end of task: in task #, " + (i + 1))
+      }
       // make task invalid if duration too large
       if (date_utils.diff(task._end, task._start, "year") > 10) {
         task.end = null;
       }
 
+
       // cache index
       task._index = i;
 
@@ -401,15 +407,16 @@ export default class Gantt {
         class: "grid-row",
         append_to: rows_layer,
       });
-
-      createSVG("line", {
-        x1: 0,
-        y1: row_y + row_height,
-        x2: row_width,
-        y2: row_y + row_height,
-        class: "row-line",
-        append_to: lines_layer,
-      });
+      if (this.options.lines === 'both' || this.options.lines === 'horizontal') {
+        createSVG("line", {
+          x1: 0,
+          y1: row_y + row_height,
+          x2: row_width,
+          y2: row_y + row_height,
+          class: "row-line",
+          append_to: lines_layer,
+        });
+      }
 
       row_y += this.options.bar_height + this.options.padding;
     }
@@ -429,6 +436,7 @@ export default class Gantt {
   }
 
   make_grid_ticks() {
+    if (this.options.lines !== 'both' && this.options.lines !== 'vertical') return
     let tick_x = 0;
     let tick_y = this.options.header_height + this.options.padding / 2;
     let tick_height =