To be proper camel case a word with no digits allowed and upto 3 upper case letters, a word:

• Must start with a lower case alphabet (a through z)
• Must have no digits (0 - 9)
• MUST have no spaces, punctuation or special characters
• Can have at most 3 uppercase alphabets in a row
• Can end in an uppercase alphabet

Notable examples

• streamIO is valid lower camel case with no digits allowed - Upto 3 upper case letters
• deviceID is valid lower camel case with no digits allowed - Upto 3 upper case letters
• serialNo is valid lower camel case with no digits allowed - Upto 3 upper case letters
• awsVPC is valid lower camel case with no digits allowed - Upto 3 upper case letters