Many things in Cov-Spectrum can be exported as embed links, PNG images or CSV files. They are all found under the "Export" button, but the code for them is actually split across different locations. Export buttons are usually shown by widgets (see ./widgets.md).
You often want to have a widget with PNG export and embed support. By using Widget.SharableComponent (see ./widgets.md) you automatically get an export button with an "Embed widget" option. To add PNG export support, put a DownloadWrapper somewhere inside your widget, around the content that you want to be exported. You can also pass csvData to DownloadWrapper, which will automatically enable CSV export.
The mechanism for showing multiple actions in the "Export" dropdown is based on React context. At the top of a subtree that can be exported (typically a Widget.SharableComponent) there is a ExportManagerContext.Provider. This provides a ExportManager object which is unique to this subtree. Anything that provides export functionality within this subtree (typically src/widgets/DownloadWrapper.tsx) registers itself with ExportManager.register(). When an ExportButton within this subtree is clicked, it fetches the latest list of registered exporters to show in the dropdown. With this design, the location of the export code and the actual export button are independent.
Sometimes you want to have plot which is not embeddable, so it is not a widget and is not rendered by Widget.SharableComponent. In this case you wont have an "Export" and may see warnings like register(...) called on ExportManager with warnOnUse. To manually add an export button, you have to add both ExportManagerContext.Provider and ExportButton. Note that the Provider must be placed outside both the button and the plot. Also, the ExportManager that you provide must be unique to the subtree. For examples, see src/components/WidgetWrapper.tsx.
If you want something other than embeds, PNG export or CSV export, you can add a custom option to the export dropdown. To do this, get the ExportManager from ExportManagerContext (from a component within ExportManagerContext.Provider) and call ExportManager.register on it. Remember to call DeregistrationHandle.deregister to avoid "leaking" menu items. See src/widgets/DownloadWrapper.tsx for an example.