--- ('---')
whitespace (' ')
tag ('!!map')
Eol ('\n')
? ('?')
whitespace (' ')
text ('a')
Eol ('\n')
indent ('  ')
: (':')
whitespace (' ')
text ('b')
Eol ('\n')
--- ('---')
whitespace (' ')
tag ('!!seq')
Eol ('\n')
- ('-')
whitespace (' ')
tag ('!!str')
whitespace (' ')
text ('c')
Eol ('\n')
--- ('---')
whitespace (' ')
tag ('!!str')
Eol ('\n')
text ('d')
Eol ('\n')
text ('e')