xAxis = g => g
.attr("font-family", "sans-serif")
.attr("font-size", 10)
.call(g => g.selectAll("g")
.data(x.ticks())
.join("g")
.each((d, i) => d.id = DOM.uid("month"))
.call(g => g.append("path")
.attr("stroke", "#000")
.attr("stroke-opacity", 0.2)
.attr("d", d => `
M${d3.pointRadial(x(d), innerRadius)}
L${d3.pointRadial(x(d), outerRadius)}
`))
.call(g => g.append("path")
.attr("id", d => d.id.id)
.datum(d => [d, d3.utcMonth.offset(d, 1)])
.attr("fill", "none")
.attr("d", ([a, b]) => `
M${d3.pointRadial(x(a), innerRadius)}
A${innerRadius},${innerRadius} 0,0,1 ${d3.pointRadial(x(b), innerRadius)}
`))
.call(g => g.append("text")
.append("textPath")
.attr("startOffset", 6)
.attr("xlink:href", d => d.id.href)
.text(d3.utcFormat("%B"))))