I think it is intended to make indexing easier for Google.

---
 main.go | 131 ++++++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 108 insertions(+), 23 deletions(-)

diff --git a/main.go b/main.go
index de770d6..c8af46b 100644
--- a/main.go
+++ b/main.go
@@ -142,7 +142,7 @@ func metricName(metric map[string]string) string {
 	return out + "{" + strings.Join(inner, ",") + "}"
 }
 
-func handleLabel(p *plot.Plot, l *plotter.Line, label string, tags map[string]string) {
+func handleLabel(p *plot.Plot, l plot.Thumbnailer, label string, tags map[string]string) {
[message trimmed]

---
 main.go | 23 +++++------------------
 1 file changed, 5 insertions(+), 18 deletions(-)

diff --git a/main.go b/main.go
index 0f4b674..de770d6 100644
--- a/main.go
+++ b/main.go
@@ -47,7 +47,7 @@ type Datapoint struct {
 }
 
 type PromResult struct {
-	Metric string
+	Metric map[string]string
[message trimmed]

---
 main.go | 247 ++++++++++++++++++++++++++++++++------------------------
 1 file changed, 143 insertions(+), 104 deletions(-)

diff --git a/main.go b/main.go
index ab164e9..0f4b674 100644
--- a/main.go
+++ b/main.go
@@ -3,9 +3,11 @@ package main
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
[message trimmed]

Rationale for this one:

The metric name was the only thing needed before I added label support, but the
label templating uses the raw tags, so it makes more sense now to preserve the
tags and render the name as needed instead of merging into into a string and
then splitting back into tags.

---
 main.go | 109 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 102 insertions(+), 7 deletions(-)

diff --git a/main.go b/main.go
index de770d6..2929767 100644
--- a/main.go
+++ b/main.go
@@ -142,7 +142,7 @@ func metricName(metric map[string]string) string {
 	return out + "{" + strings.Join(inner, ",") + "}"
 }
 
-func handleLabel(p *plot.Plot, l *plotter.Line, label string, tags map[string]string) {
+func handleLabel(p *plot.Plot, l plot.Thumbnailer, label string, tags map[string]string) {
[message trimmed]

---
 main.go | 23 +++++------------------
 1 file changed, 5 insertions(+), 18 deletions(-)

diff --git a/main.go b/main.go
index 0f4b674..de770d6 100644
--- a/main.go
+++ b/main.go
@@ -47,7 +47,7 @@ type Datapoint struct {
 }
 
 type PromResult struct {
-	Metric string
+	Metric map[string]string
[message trimmed]

---
 main.go | 247 ++++++++++++++++++++++++++++++++------------------------
 1 file changed, 143 insertions(+), 104 deletions(-)

diff --git a/main.go b/main.go
index ab164e9..0f4b674 100644
--- a/main.go
+++ b/main.go
@@ -3,9 +3,11 @@ package main
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
[message trimmed]

---
 README.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/README.md b/README.md
index e79a46f..c4e192d 100644
--- a/README.md
+++ b/README.md
@@ -35,5 +35,8 @@ set the query parameters as appropriate:
 - **width**, **height**: adjust chart dimensions in inches
 - **step**: number of seconds between data points
 - **min**, **max**: Y axis limits
+- **label**: template for the chart legend in Go's text/template format. All
+values provided by prometheus as tags are available - to label each matching
[message trimmed]

---
 main.go | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/main.go b/main.go
index c1ffa77..ab164e9 100644
--- a/main.go
+++ b/main.go
@@ -186,12 +186,6 @@ func registerExtension(router chi.Router, extension string, mime string) {
 			height = vg.Length(h) * vg.Inch
 		}
 
-		// Undocumented option
-		var legend string
[message trimmed]