Purpose of adding a dummy whitespace at the beginning of each line of sentence

[frankxu2004]

I have seen in the help text of spm_train the following about the parameter:

--add_dummy_prefix (Add dummy whitespace at the beginning of text) type: bool default: true

Is there any explanation that why the default behavior is adding a prefix whitespace? I am just wondering what's the intention or advantages of doing this.

[taku910]

We would like to make the same treatment for the following two sentences

world
Hello world

Both are converted to

_world
_Hello_world

"_world" tends to be extracted as one token by putting a dummy whitespace.

[frankxu2004]

Cool! that is actually intriguing!

[taku910]

Seems the issue was resolved. closing.