Reads indentation based on the number of TAB characters in the given indented
text. Adapts the read indentation based on the indentation of the previous
line and on the previous node. The following adaptation algorithm is used:
- if the indentation of the current line is greater than that of the
previous line, then the indentation of the current line is the indentation of
the previous line plus 1
- if the indentation of the previous line is 0 or if there is no previous
node, then the indentation of the current line will be 0