On realworldocaml.org, find the 'Ref cells' section within the 'Imperative Programming' chapter. Explain what a ref cell is in OCaml and provide the OCaml code to initialize a ref cell with the integer value 5 and then update its value to 10.
Navigate to 'realworldocaml.org'. From the homepage, click on 'Imperative Programming' under 'Language Concepts'. On the 'Imperative Programming' page, click on 'Mutable Record and Object Fields and Ref Cells' under 'Primitive Mutable Data'. Locate the 'Ref cells' subsection. Extract the explanation of ref cells and the OCaml code for initializing a ref with 5 and updating it to 10.
The explanation clearly states that 'Ref cells' are used for mutable variables in OCaml, acting as containers for a single mutable value. The provided OCaml code for initializing a ref with the value 5 is `let x = ref 5;;`. The provided OCaml code for updating the ref's value to 10 is `x := 10;;`.