Some, but not all, of your library entry data can be searched within your Mendeley Reference Manager library.
The following are searchable within your Mendeley library (including when within collections, folders and groups.)
The following are NOT searchable within your Mendeley Reference Manager library
The newer downloadable software tool from Mendeley, Reference Manager, has an annotation feature (Notebook) that allows you to collect your notes and highlighted text (quotations) from multiple items in your Mendeley library. Check the support page for the latest Notebook and other annotation features.