Custom Variables in Debug Visual

Do these work?  I've tried copying the sample from the barchart tutorial (https://github.com/Microsoft/PowerBI-visuals/blob/master/Tutorial/StaticObjects.md) yet the items i add  never appear under the "format" pane.  Am i missing something?  My capabilities.json looks like this (below) and i was expecting to see an 'Enable Axis' option under formatting on the right?  Apologies if i have missed something.

{
"dataRoles": [
{
"displayName": "Category Data",
"name": "category",
"kind": 0
},
{
"displayName": "Measure Data",
"name": "measure",
"kind": 1
}
],
"dataViewMappings": [
{
"conditions": [
{
"category": {
"max": 1
},
"measure": {
"max": 1
}
}
],
"categorical": {
"categories": {
"for": {
"in": "category"
}
},
"values": {
"select": [
{
"bind": {
"to": "measure"
}
}
]
}
}
}
],
"objects": {
"enableAxis": {
"displayName": "Enable Axis",
"properties": {
"show": {
"displayName": "Enable Axis",
"type": { "bool": true }
}
}
}
}
}