endOfColumns
Skips leading whitespace for as long as it spans fewer than columns columns, counting a tab up to the next TAB_WIDTH stop. A tab is never split: it is taken whole or not at all, which is why the limit is reached exactly when it is a multiple of TAB_WIDTH.
Return
index just past the skipped whitespace
Parameters
source
text to inspect
start
index of the slice's first character
end
index just past the slice's last character
columns
how many columns of whitespace to skip at most