What does a double colon mean in a shell script?

This is the code development style, in fact, is a function name, equivalent to the underscore division, but read into the package name after the meaning of different. This is defined in accordance with Google's shell development specifications.

Reference:

Https://google.github.io/styleguide/shell.xml?showone=Function_Names#Function_Names

http://stackoverflow.org.cn/front/ask/view?ask_id=557361

Https://stackoverflow.com/questions/44558080/what-are-double-colons-in-a-shell-script

What does a double colon mean in a shell script?