Creating a String Variable

Is it possible to create and use a Lvar string variable like (L:Str_Var,string) in a formatted text element like so:
   <Visible>(L:display_text, bool)</Visible>
     <Position X="265" Y="125"/>
     <FormattedText X="84" Y="26" Length="4" Bright="Yes" FontSize="26" Font="Arial Bold" Color="White" Adjust="Left" VerticalAdjust="Top" Multiline="No">
If so, what is the syntax for loading a string, like "TEST", into (L:Str_Var,string) ?

No. L:Vars can accommodate numbers only.

A few ways to handle strings is discussed in this FSDeveloper Wiki - Storing Strings.

There is also a general discussion about strings found in the gps module guidebook starting on page 202.

Finally, search for "strings" in this site and you'll find lots of XML examples.

Hope this helps.