You can have a Text Area with multiple lines of text if you separate each line with '\n'. You can have a Text Area with indented lines if you put '\t' before the line.
Note for examples below: To switch views between the Active Form and Markup Code, click on "View" in the upper right of this page. Then choose "Form" to see the Active Form or choose "Markup" to reveal the Markup Code.
Example 1: [textarea name="variable_1" memo="multiple lines of default text" default="line 1\nline 2\nline 3\nline 4"]
Example 2: [textarea name="variable_2" memo="multiple lines of default text with indent" default="sample text\nsample2\n\tindented\nback again"]