You can refine a search with logical operators.

~near (within about 100 characters)
( )precedence
#word break

And you can restrict a search to set of authors or works by including filters in the search string. Filters use abbreviations (or numbers) for authors and works and are enclosed within square brackets. For example, [Cic] esse videtur would search for esse videtur in Cicero. These patterns are valid:

[Cic:Catil]Cicero's In Catilinam
[Cic:56-59]Cicero's Letters
[474:39-40,73]Brutus, Orator, and Rhetorica ad Herennium
[Cic Quint]Cicero and Quintilian
[Catul Tib Prop Ov]Catullus, Tibullus, Propertius, and Ovid

Abbreviations (and numbers) can be found in the Canon.