User-Editable R Functions in 'Shiny' Apps with a Step Debugger // A pair of 'Shiny' modules that let end users of a 'Shiny' application author their own R functions directly in the browser. Host apps can expose these modules as extension points where user-supplied code augments or replaces built-in logic, without requiring users to modify the app's source. Each module embeds an 'Ace' editor with a structured argument table, an in- frame R console rooted in the paused function's local environment, and a step debugger that handles for, while, repeat, and if/else blocks at any nesting depth. Two module flavours are provided: solo editors for testing a function in isolation with literal argument values, and embedded editors for pausing a function mid-execution inside a larger host program.