YAML Multiline Strings: Find the right syntax for your YAML multiline strings
There are two types of formats that YAML supports for strings: block scalar and flow scalar formats. (Scalars are what YAML calls basic values like numbers or strings, as opposed to complex types like arrays or objects.) Block scalars have more control over how they are interpreted, whereas flow scalars have more limited escaping support.
Source: YAML Multiline Strings
This is a handy tool.