For Example:
1,Create document which include two arrays that array "b" contain "name" attribute like "a"
db.test.insert(
{
"a":[

{"name":"a","age":"99"}

,

{"name":"b","age":"99"}

],
"b":[

{"level":"a","name":"a","age":"99"}

,

{"level":"b","name":"b","age":"99"}

]}
)

2,Update document which I want locate

{"name":"a","age":"99"}

in "a" and

{"level":"b","name":"b","age":"99"}

in "b"
db.test.update(

{"a.name":"a","b.level":"b"}

,
{"$set":{"a.$.age":"100","b.$.age":"100"}}
)

But the result is:
{"_id":ObjectId("53437c573de4c79e7ff69e91"),
"a":[

{"name":"a", "age":"99" }

,

{"age":"100","name":"b"}

],
"b":[

{"level":"a","name":"a","age":"99"}

,

{"age":"100","level":"b","name" :"b"}

]
}
Updated the "

{ "age" : "100", "name" : "b" }

" in "a" like above ...