The highest tagged major version is v4.

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Valid go.mod file

The Go module system was introduced in Go 1.11 and is the official dependency management solution for Go.
Redistributable license

Redistributable licenses place minimal restrictions on how software can be used, modified, and redistributed.
Tagged version

Modules with tagged versions give importers more predictable builds.
Stable version

When a project reaches major version v1 it is considered stable.
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Path	Synopsis
asn1-ber.v1
ldap.v2 Package ldap provides basic LDAP v3 functionality.	Package ldap provides basic LDAP v3 functionality.
yaml.v2 Package yaml implements YAML support for the Go language.	Package yaml implements YAML support for the Go language.