Meagan Longoria has started a series on Biml code nuggets and has started with text nuggets:
Text nuggets evaluate the expression they contain and then replace the text nugget with the string representation of the value of the expression. I use them often to switch out names of packages, tasks, and components as well as source and destination tables in SSIS development when creating packages based upon a design pattern.
Text nuggets start with <#= and end with #>. Notice there is an equals sign at the beginning of the text nugget but not at the end.
Text nuggets are very useful. You can include complex business logic in the expressions. And the expression result can be any data type. The BimlScript compiler will automatically convert it to text before replacing the code nugget with the result. Like all code nuggets, text nuggets can be a single line or multiple lines.
Read the whole thing.