1.1.1 style numbering

[pessoa]

How do I format an ouline like this?

1 Heading
1.1 Subheading
1.1.2 sub-sb

2 Second Heading
2.1 Sub-heading
2.1.2 etc.

 

[Rainald Taesler]

How do I format an ouline like this?

1 Heading
1.1 Subheading
1.1.2 sub-sb

2 Second Heading
2.1 Sub-heading
2.1.2 etc.

Obviously this type of format is missing [siiiigh].
Serious omission IMO.

Rainald