The Source Text property of a text layer is interpreted by expressions as a JavaScript String. You can use the pick whip to retrieve the source text from another text layer; however, only the style of the first character of the destination layer is used.

For more information on the String object, consult a JavaScript guide.

You can use "\r" in a string expression to start a new line of text. For example, to copy the original text from one layer onto the same layer and repeat it in all uppercase characters on a new line, use the following expression:

  text.sourceText + "\r" + text.sourceText.toUpperCase()

Adding a text layer to a composition and adding an expression to its Source Text property can be a great way to examine the property values of other layers. For example, the following expression on a Source Text property reports the name and value of the Opacity property for the next layer in the layer stacking order:

  thisComp.layer(index + 1).name + "\rOpacity = " + thisComp.layer(index + 1).opacity.value

The following example reports the name of the footage item used as the source of the topmost image layer in the stacking order at the current time that has its Video switch set.

  source_footage_name = ""; 
  for (i = 1; i <= thisComp.numLayers; i++){ 
      if (i == index) continue; 
      my_layer = thisComp.layer(i); 
      if (! (my_layer.hasVideo && my_layer.active)) continue; 
      if (time >= my_layer.inPoint && time < my_layer.outPoint){ 
          try{ 
              source_footage_name = my_layer.source.name; 
          }catch(err1){ 
              source_footage_name = my_layer.name 
          } 
          break; 
      } 
  } 
  source_footage_name