coerce tickson,

... only on `type: 'category'` cartesian axes with
    visible ticks and/or grid lines.

Author: etpinard

src/components/colorbar/draw.js

@@ -198,6 +198,7 @@ module.exports = function draw(gd, id) {
                 letter: 'y',
                 font: fullLayout.font,
                 noHover: true,
+                noTickson: true,
                 calendar: fullLayout.calendar  // not really necessary (yet?)
             };
 

src/plots/cartesian/axis_defaults.js

@@ -28,6 +28,7 @@ var setConvert = require('./set_convert');
  *  outerTicks: boolean, should ticks default to outside?
  *  showGrid: boolean, should gridlines be shown by default?
  *  noHover: boolean, this axis doesn't support hover effects?
+ *  noTickson: boolean, this axis doesn't support 'tickson'
  *  data: the plot data, used to manage categories
  *  bgColor: the plot background color, to calculate default gridline colors
  */
@@ -89,5 +90,10 @@ module.exports = function handleAxisDefaults(containerIn, containerOut, coerce,
 
     if(options.automargin) coerce('automargin');
 
+    if(!options.noTickson &&
+        containerOut.type === 'category' && (containerOut.ticks || containerOut.showgrid)) {
+        coerce('tickson');
+    }
+
     return containerOut;
 };

src/plots/cartesian/layout_attributes.js

@@ -304,6 +304,19 @@ module.exports = {
             'the axis lines.'
         ].join(' ')
     },
+    tickson: {
+        valType: 'enumerated',
+        values: ['labels', 'boundaries'],
+        role: 'info',
+        editType: 'ticks',
+        description: [
+            'Determines where ticks and grid lines are drawn with respect to their',
+            'corresponding tick labels.',
+            'Only has an effect for axes of `type` *category*.',
+            'When set to *boundaries*, ticks and grid lines are drawn half a category',
+            'to the left/bottom of labels.'
+        ].join(' ')
+    },
     mirror: {
         valType: 'enumerated',
         values: [true, 'ticks', false, 'all', 'allticks'],

src/plots/gl3d/layout/axis_defaults.js

@@ -50,6 +50,7 @@ module.exports = function supplyLayoutDefaults(layoutIn, layoutOut, options) {
                 letter: axName[0],
                 data: options.data,
                 showGrid: true,
+                noTickson: true,
                 bgColor: options.bgColor,
                 calendar: options.calendar
             },