1. A computer recordable medium, having a computer readable program encoded thereon and being directly loadable into a working memory of a data processing system, the computer readable program having instructions for performing a method of editing program code when the computer readable program is run on the data processing system, the program code being suitable for subsequent processing, wherein the method comprises: defining at least two portions of the program code; selecting a first defined portion of the at least two portions of the program code, wherein the first defined portion is a service instruction portion; compressing a representation of the first defined portion in a visual representation of the program code such that content of the first defined portion is not visible in the visual representation of the program code, wherein a second defined portion of the at least two portions of the program code remains visible in the visual representation of the program code; automatically disabling the first defined portion, the disabled first defined portion being excluded from the subsequent processing, wherein the second defined portion is subjected to subsequent processing, and wherein disabling the first defined portion comprises automatically converting the service instructions in the first defined portion to comments in the program code by inserting comment tags in association with the service instructions; receiving an input to re-enable the first defined portion; and automatically re-enabling the first defined portion in response to receiving the input, wherein re-enabling the first defined portion comprises removing the comment tags associated with the service instructions, wherein compressing the representation of the first defined portion in the visual representation of the program code comprises: replacing a visual representation of the content of the first defined portion with an identifier of the first defined portion, the identifier indicating a position in the program code where the first defined portion was present but not containing contents of the first defined portion; and inserting, into the visual representation of the program code, an compression identifier in association with the identifier of the first defined portion, the compression identifier indicating that the first defined portion has been compressed.