1. A computer-readable medium having computer-executable instructions for causing a computer to perform steps comprising: receive input from a user to generate an add-in bridge; programmatically determine one or more requirements that an add-in is required to implement in order to integrate with a particular host, the one or more requirements being a static set of requirements that are part of a static extensibility model; and programmatically generate the add-in bridge to conform to the one or more requirements of the particular host and to operate like a compiled add-in while actually calling one or more script files that are executed by at least one scripting engine to implement a desired functionality, the one or more script files being written in a dynamic language.