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[a-z])+([0-9]+)([a-z]+

Answer:

No.. the parentheses are not balanced.

Nested Groups

Regular Expression
String
Group 0
Group 1	Group 2	Group 3	Group 4

Capture groups may be nested. A group consists of a left parenthesis and whatever is included up to its matching right parenthesis. This means that the characters that are captured by one group may also belong to another group.

([a-z]+)([0-9]+)([a-z]+)

Group numbering works as before:

Group 0 is the entire substring matched by the RE.
Group 1 is the group formed by the first left parenthesis and its right parenthesis mate, regardless of whatever groups are contained between them.
Group 2 is the group fromed by the second left parenthses and its right partenthesis mate, regardless of whatever groups are contained between them.

QUESTION 12:

Examine the following:

(((rat )bat )cat )(dog)

What subexpression does group 4 consist of?