You must know:
contenteditable, in particular the little range/caret navigation (DOM/Range interfaces) differences between the browsers.
Polymer knowledge is an advantage but not a must.
The idea behind the app/component is to develop a text editor based on and extendable via custom elements. It's 95% complete in Chrome, but still needs some tuning and crossbrowser love.
Your job will be to polish caret navigation issues.
This is about an open source project, so you might be interested to join as a collaborator/maintainer.
The offer is intended for single developers unless you are a company willing to collaborate on and benefit from the project via contribution of finances and/or development time.