I could describe what an Annotation is, but it's easier to show it:

using Term.Annotations

    "This is the main text to annotate",
    "main"=>"by main we mean most important, the rest is annotations",
    "annotate"=>"annotations are just extra bits of info"
This is the main text to annotate                             
            ──┬─         ────┬───                             
              ╰─│  by main we mean most important,           
                  the rest is annotations                   
                             ╰─│  annotations are just       
                                 extra bits of info         

as you can see, Panels with extra messages are displayed underneath the main bit of text. Each "annotation" is defined by Pair, the first element of the Pair is a substring of the main text indicating what we want to annotate. The second element is used to specify what we want to annotate it with.

If you want to assign some Style information to each annotation, you can specify that by using a Tuple{String, String} as second element of the Annotation Pair. In this tuple, the first part refers to the annotation message while the second can store style information.

Annotation("this has some style", "style"=>("style means color or stuff like bold", "bold red"))
this has some style                                         
                ╰─│  style means color or stuff like bold  

and of course you can mix your normal markup style too: Annotation("{bold italic}this{/bold italic} has some style", "style"=>("style means {brightblue}color{/brightblue} or stuff like {bold}bold{/bold}", "bold red")).

Annotation objects are AbstractRenderables, so you can mix and match them with other things too.

import Term: Panel, highlight_syntax

code = highlight_syntax("Annotation(\"main text\", \"main\"=>\"most important\")")

    Annotation(code, "\"main text\""=>"main message to be annotated", "\"main\"=>\"most important\""=>"annotation");
    padding=(4, 4, 2, 1),
    title="Annotation: usage", fit=true, title_style="default green bold",
    title_justify=:center, style="green dim"
╭────────────────────── Annotation: usage ─────────────────────╮
    Annotation("main text", "main"=>"most important")         
               ─────┬─────  ────────────┬───────────          
                    ╰─│  main message to be annotated        
                                        ╰─│  annotation