What is the use of the pipe symbol in YAML?

I am new to yaml, and I have a question about the pipe symbol (|) used for multiple lines. Does YAML have any syntax like the one below?

test: |6+

Of the two YAML files below, the first one is working and second is not. I do not know what is causing this.

First File

Name :
  -
   testing:

     val1
  -
   second:
     val2
  -
   third:
     val3
  -
   then
  - 

    final: |
     a
     aa
     aaa
     aaaa : 'test:'

Second File

Name :

  -
   testing:
     val1
  -
   second:
     val2
  -
   third:
     val3
  -

   then
  - 
    final: |6+
      a
      aa
      aaa
      aaaa : 'test:'

The second file is the customer's.

I am using XMLBeans and I get this error:

com.esotericsoftware.yamlbeans.parser.Parser$ParserException: Line 17, column 12: Expected a 'block end' but found: block mapping start".