Brown-Driver-Briggs has a helpful article on יֵשׁ on page 441.
See Gesenius-Kautzsch §116s, or Joüon-Muraoka §154c regarding the omission of the pronominal subject from nominal clauses. See also the post on the Derived Stems found under the Hebrew 101 link for a reminder about the Pual.
Be sure to watch the video on Nominal and Verbal Clauses under the Featured Topics on Syntax link in conjunction with this video.
In Ruth 1:4b we have 2 nominal clauses. See my video on Nominal Clauses for a refresher.
In this video I introduce verbal clauses and explain how they differ in meaning from nominal clauses.