will match the complete word with no alphanumeric and
_ preceding or following by it.
Taking from regularexpression.info
There are three different positions that qualify as word boundaries:
- Before the first character in the string, if the first character is a word character.
- After the last character in the string, if the last character is a word character.
- Between two characters in the string, where one is a word character and the other is not a word character.
The term word character here means any of the following
In short, word character =