1. Introduction  
2. The Mg ii sample  
2.1. MUSE Observations and Spectral Measurements  
2.2. Sample Selection  
2.3. Sample Classification  
2.4. Observational Properties from HST Photometry and Imaging  
3. Nebular Emission Features in Mg ii Emitters  
3.1. Photoionization Models of Star-forming Galaxies  
3.2. Comparison with Observations in Mg ii Emitters  
3.3. Contribution from Other Ionizing Sources  
4. Spectral Fitting Analysis and Results  
4.1. Spectrophotometric Fitting Tool Beagle  
4.2. Beagle Fitting to the Mg ii Parent Sample  
4.3. Beagle Results  
5. Discussion  
5.1. Predictions from Photoionization Models  
5.2. Mg ii Emitters versus Absorbers  
5.3. Mg ii as an Analogy to Ly α  
5.4. Mg ii Escape Fraction  
6. Summary and Conclusions