An skEdit bundle can define a code-completion dictionary. This dictionary will be used to provide hints as you type, decreasing the amount of typing that you have to do. skEdit can either provide the hints automatically as you type, or manually by hitting the F5 key. This can be controlled in the Code Completion pref pane.
In addition to the built-in dictionary, if a bundle defines a code index dictionary, skEdit will index your files and include classes, functions, etc. from your files in the code completion hints. The index is updated when a project or file is opened and when a file is saved. skEdit will try to only show items that the current file references. For example, an HTML file that references a CSS file will show the CSS classes from that file, but not from an unreferenced file.