Lines and Folds

 A line in AE can be upto 500 characters long and may be of 4 main types :-

      Text line           A list of characters.

      Fold line           A tagged list of lines, shown as :-

                          ... tag

                          or :-

                          {{{ tag
                              contents of fold
                              more contents
                              ... tag of sub-fold
                              last line of fold
                          }}}

      Virtual fold line   A link to another file with a tag, shown as :-

                          ::: filename tag

                          or :-

                          >>> filename tag

                          The first word after the ::: or >>> is
                          the filename, the rest of the line is the tag.

      Terminator line     The last line in a fold is shown like this :-

                          ^

 With the fold and virtual fold, the ..., {{{, ::: and >>> parts are not part
 of the line but merely indicate the line type. This explains why these parts
 cannot be edited. Searching will ignore these first little bits and the
 left-anchor in regular expressions will match the text after them.

 If you press space or tab before or on these parts, the whole fold or
 virtual fold is indented, and can also be un-indented by deleting the
 imaginary characters before the ... etc.

 eg:  Before indent                      After indent

      ~                                  ~
      ~                                  ~
      if ((fp=fopen("x","r"))==NULL)     if ((fp=fopen("x","r"))==NULL)
      {{{ die                                    {{{ die
      {                                          {
      ... closedown                              ... closedown
      fputs("arrggh!\n", stderr);                fputs("arrggh!\n"), stderr);
      exit(1);                                   exit(1);
      }                                          }
      }}}                                        }}}
      c = getc(fp);                      c = getc(fp);
      ^                                  ^
      ~                                  ~
      ~                                  ~

 When in one fold, sub-folds are treated as if they were one line, always!

 Folds and virtual folds can be open or closed, hence the 2 forms of display
 for each. Open folds are displayed along with their contents (like in the
 'die' fold above), whereas closed folds are simply shown as ... tag (like
 the 'closedown' fold above).

 Virtual folds are never displayed along with their contents since the
 contents are held in another file, which may not be being edited. This does
 not make the open/closed status redundant as the searching commands may be
 made to search just open virtual folds.

 By the use of virtual folds, it is possible to edit many files as easily as
 editing one.