appendVariable 
  Builder-function that appends a variable (${VAR}) to the {@linkcode SnippetString.value value} of this snippet string.
Parameters
name
The name of the variable - excluding the $.
defaultValue 
The default value which is used when the variable name cannot be resolved - either a string or a function with which a nested snippet can be created.
fun appendVariable(name: String, defaultValue: (snippet: SnippetString) -> Unit): SnippetString(source)