a query on example of PKCS#7 object

hi, 

I was going through the following example of Signed data with attributes. 

can someone tell me what the numbers and colon (:) in left side denotes... 

as per pkcs#7 document following is the defination of signed data. From this
definition it is not clear what the bumbers and colon(:) on left side
denote.

Will highly appreciate for your time to reply this query. 


thank you, 

pradeep 

9.1 SignedData type 


The signed-data content type shall have ASN.1 type SignedData:

SignedData ::= SEQUENCE {
  version Version,
  digestAlgorithms DigestAlgorithmIdentifiers,
  contentInfo ContentInfo,
  certificates
        [0] IMPLICIT ExtendedCertificatesAndCertificates
       OPTIONAL,
  crls
    [1] IMPLICIT CertificateRevocationLists OPTIONAL,
  signerInfos SignerInfos } 
DigestAlgorithmIdentifiers ::=
  SET OF DigestAlgorithmIdentifier 
SignerInfos ::= SET OF SignerInfo 

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