59.4 Garbage in the Text
If C-l shows that the text is wrong, try undoing the changes to it
using C-x u until it gets back to a state you consider correct. Also
try C-h l to find out what command you typed to produce the observed
results.
If a large portion of text appears to be missing at the beginning or
end of the buffer, check for the word ‘Narrow’ in the mode line.
If it appears, the text you don't see is probably still present, but
temporarily off-limits. To make it accessible again, type C-x n
w. See Narrowing.