channel method
Sets a channel that every mark on this view inherits.
name The channel name.
field The column name.
Returns This chart, so calls chain.
Implementation
VlChart channel(String name, String field) {
VlJson ch = VlJson.objectValue();
ch.setMember("field", VlJson.stringValue(field));
this.enc.setMember(name, ch);
cursor = name;
return this;
}