[abc] | 
              A single character of: a, b or c | 
             
            
              [^abc] | 
              Any single character except: a, b, or c | 
             
            
              [a-z] | 
              Any single character in the range a-z | 
             
            
              [a-zA-Z] | 
              Any single character in the range a-z or A-Z | 
             
            
              ^ | 
              Start of line | 
             
            
              $ | 
              End of line | 
             
            
              \A | 
              Start of string | 
             
            
              \z | 
              End of string | 
             
          
         
       | 
      
        
          
            
              . | 
              Any single character | 
             
            
              \s | 
              Any whitespace character | 
             
            
              \S | 
              Any non-whitespace character | 
             
            
              \d | 
              Any digit | 
             
            
              \D | 
              Any non-digit | 
             
            
              \w | 
              Any word character (letter, number, underscore) | 
             
            
              \W | 
              Any non-word character | 
             
            
              \b | 
              Any word boundary | 
             
          
         
       | 
      
      
        
          
            (...) | 
            Capture everything enclosed | 
           
          
            (a|b) | 
            a or b | 
           
          
            a? | 
            Zero or one of a | 
           
          
            a* | 
            Zero or more of a | 
           
          
            a+ | 
            One or more of a | 
           
          
            a{3} | 
            Exactly 3 of a | 
           
          
            a{3,} | 
            3 or more of a | 
           
          
            a{3,6} | 
            Between 3 and 6 of a | 
           
        
       
     |