Recent integrated development environments (IDEs) have become more extensible tool platforms but it is in fact hard for non-experts to extend or customize them. This paper proposes a mechanism for adding new functionalities to existing IDEs by using two kinds of XML-based configurations. One of them defines relationships between code fragments and the other determines how these relationships are utilized. In these configurations, a user can flexibly combine two kinds of components. They encapsulate either a trigger which expresses when the added functionality is performed or an action which is actually performed due to the trigger. Therefore, the user easily attains the extension of IDEs without knowing programming techniques by only writing XML-based configurations. The experimental results with a prototype of the proposed system show the reduction of efforts to understand proprietary APIs provided by IDEs.