When using slopes it is often desired to add some labelling to express what they represent. Currently the implementation of Slope does not seem to support legend labelling which raises the question if this is an intentional choice (i.e. due to Slope being different than regular glyphs) or just a lacking feature?
Yes and no.
Slope is an annotation, not a glyph, and there are definitely things about annotations that are intentionally different from glyphs. But it’s reasonable to want to include annotations in legends so for this specific question I think mostly it’s just a case of “no one has gotten around to making it happen yet”. There are a couple of existing relevant issues:
- [FEATURE] Allow BoxAnnotations in Legends · Issue #12117 · bokeh/bokeh · GitHub
- [FEATURE] GlyphLegendItem for arbitrary legend items · Issue #10776 · bokeh/bokeh · GitHub
Either of those could be a path towards including legend items for annotations (i.e. that match their visuals).