add some comments

backend/playbackmanager.go

@@ -18,6 +18,9 @@ const (
 	ReplayGainTrack = string(player.ReplayGainTrack)
 )
 
+// A high-level Subsonic-aware playback backend.
+// Manages loading tracks into the Player queue,
+// sending callbacks on play time updates and track changes.
 type PlaybackManager struct {
 	ctx           context.Context
 	cancelPollPos context.CancelFunc

backend/servermanager.go

@@ -85,10 +85,12 @@ func (s *ServerManager) Logout() {
 	}
 }
 
+// Sets a callback that is invoked when a server is connected to.
 func (s *ServerManager) OnServerConnected(cb func()) {
 	s.onServerConnected = append(s.onServerConnected, cb)
 }
 
+// Sets a callback that is invoked when the user logs out of a server.
 func (s *ServerManager) OnLogout(cb func()) {
 	s.onLogout = append(s.onLogout, cb)
 }

backend/updatechecker.go

@@ -9,6 +9,8 @@ import (
 	"time"
 )
 
+// A component to check for updates from the
+// Github releases/latest URL.
 type UpdateChecker struct {
 	OnUpdatedVersionFound func()
 
@@ -26,6 +28,8 @@ func NewUpdateChecker(appVersionTag, latestReleaseURL string, lastCheckedTag *st
 	}
 }
 
+// Start automatically polling for updates in the background.
+// Quits when the given ctx's Done channel returns a value.
 func (u *UpdateChecker) Start(ctx context.Context, interval time.Duration) {
 	go func() {
 		u.checkForUpdate() // check once at startup

ui/widgets/auxcontrols.go

@@ -8,6 +8,8 @@ import (
 	"fyne.io/fyne/v2/widget"
 )
 
+// The "aux" controls for playback, positioned to the right
+// of the BottomPanel. Currently only volume control.
 type AuxControls struct {
 	widget.BaseWidget
 

ui/widgets/imageplaceholder.go

@@ -11,6 +11,9 @@ import (
 	"fyne.io/fyne/v2/widget"
 )
 
+// A widget that can display an image or else
+// a placeholder with a rectangular border frame
+// and an icon positioned in the center of the frame.
 type ImagePlaceholder struct {
 	widget.BaseWidget
 	container *fyne.Container

ui/widgets/listrowbase.go

@@ -14,6 +14,7 @@ var _ fyne.Tappable = (*ListRowBase)(nil)
 var _ fyne.Widget = (*ListRowBase)(nil)
 var _ fyne.Focusable = (*ListRowBase)(nil)
 
+// Base type used for all list rows in widgets such as Tracklist, etc.
 type ListRowBase struct {
 	widget.BaseWidget
 

ui/widgets/nowplayingcard.go

@@ -10,6 +10,8 @@ import (
 	"fyne.io/fyne/v2/widget"
 )
 
+// Shows the current album art, track name, artist name, and album name
+// for the currently playing track. Placed into the left side of the BottomPanel.
 type NowPlayingCard struct {
 	widget.BaseWidget
 

ui/widgets/textrestrictedentry.go

@@ -8,6 +8,8 @@ import (
 	"fyne.io/fyne/v2/widget"
 )
 
+// A widget.Entry that allows restrictions on the text
+// that can be typed into it, based on a charAllowed callback.
 type TextRestrictedEntry struct {
 	widget.Entry
 

ui/widgets/togglebuttongroup.go

@@ -8,6 +8,9 @@ import (
 	"fyne.io/fyne/v2/widget"
 )
 
+// Lays out multiple buttons horizontally with no padding,
+// and uses button.Importance to highlight exactly one which is "active".
+// Similar to a segmented control in other UI toolkits.
 type ToggleButtonGroup struct {
 	widget.BaseWidget
 

ui/widgets/toggletext.go

@@ -6,6 +6,9 @@ import (
 	"fyne.io/fyne/v2/widget"
 )
 
+// Similar to widgets.ToggleButtonGroup, but using text.
+// The "active" label is bolded non-interactive text,
+// while all the others are hyperlinks.
 type ToggleText struct {
 	widget.BaseWidget