Hi, I made uiEntrySetPlaceholder for my app. (You can see the commit on my branch.)
It can set text to be displayed in the entry when it's empty.
like this.

The functions are so simple cause the native controls support placeholders.
And we can use the similar methods for most of the controls that have text entries.

The problem is winapi doesn't support placeholders for multi-line entries and read-only entries.
So, we need to implement them by ourselves if we want. (I don't want to work on it tho.)
But it's worthy to add the placeholder functions to libui even if they will ignore some controls that winapi doesn't support, I think.

If you like it, I will send PR after adding the placeholder support for some controls.