New startup options, #+startup: show<n>levels

* lisp/org.el (org-startup-folded, org-startup-options)
  (org-set-startup-visibility): Add new startup options

doc/org-guide.org

@@ -169,8 +169,8 @@ Org uses just two commands, bound to {{{kbd(TAB)}}} and
 When Emacs first visits an Org file, the global state is set to
 OVERVIEW, i.e., only the top level headlines are visible.  This can be
 configured through the variable ~org-startup-folded~, or on a per-file
-basis by adding a =STARTUP= keyword to =overview=, =content=, or
-=showall=, like this:
+basis by adding a =STARTUP= keyword to =overview=, =content=,
+=showall=, =showeverything= or =show<n>levels= (n = 2..5) like this:
 
 : #+STARTUP: content
 

doc/org-manual.org

@@ -578,6 +578,10 @@ buffer:
 ,#+STARTUP: overview
 ,#+STARTUP: content
 ,#+STARTUP: showall
+,#+STARTUP: show2levels
+,#+STARTUP: show3levels
+,#+STARTUP: show4levels
+,#+STARTUP: show5levels
 ,#+STARTUP: showeverything
 #+end_example
 
@@ -18960,6 +18964,10 @@ changes.
   | =overview=       | Top-level headlines only.  |
   | =content=        | All headlines.             |
   | =showall=        | No folding on any entry.   |
+  | =show2levels=    | Headline levels 1-2.       |
+  | =show3levels=    | Headline levels 1-3.       |
+  | =show4levels=    | Headline levels 1-4.       |
+  | =show5levels=    | Headline levels 1-5.       |
   | =showeverything= | Show even drawer contents. |
 
   #+vindex: org-startup-indented

etc/ORG-NEWS

@@ -112,6 +112,12 @@ package, to convert pandas Dataframes into orgmode tables:
 | 2 | 3 | 6 |
 #+end_src
 
+*** New startup options =#+startup: show<n>levels=
+
+These startup options complement the existing =overview=, =content=,
+=showall=, =showeverything= with a way to start the document with n
+levels shown, where n goes from 2 to 5.
+
 *** New =u= table formula flag to enable Calc units simplification mode
 
 A new =u= mode flag for Calc formulas in Org tables has been added to

lisp/org.el

@@ -939,6 +939,7 @@ the following lines anywhere in the buffer:
    #+STARTUP: fold              (or `overview', this is equivalent)
    #+STARTUP: nofold            (or `showall', this is equivalent)
    #+STARTUP: content
+   #+STARTUP: show<n>levels (<n> = 2..5)
    #+STARTUP: showeverything
 
 Set `org-agenda-inhibit-startup' to a non-nil value if you want
@@ -949,6 +950,10 @@ time."
   :type '(choice
 	  (const :tag "nofold: show all" nil)
 	  (const :tag "fold: overview" t)
+	  (const :tag "fold: show two levels" show2levels)
+	  (const :tag "fold: show three levels" show3levels)
+	  (const :tag "fold: show four levels" show4evels)
+	  (const :tag "fold: show five levels" show5levels)
 	  (const :tag "content: all headlines" content)
 	  (const :tag "show everything, even drawers" showeverything)))
 
@@ -4121,6 +4126,10 @@ After a match, the following groups carry important information:
     ("overview" org-startup-folded t)
     ("nofold" org-startup-folded nil)
     ("showall" org-startup-folded nil)
+    ("show2levels" org-startup-folded show2levels)
+    ("show3levels" org-startup-folded show3levels)
+    ("show4levels" org-startup-folded show4levels)
+    ("show5levels" org-startup-folded show5levels)
     ("showeverything" org-startup-folded showeverything)
     ("content" org-startup-folded content)
     ("indent" org-startup-indented t)
@@ -6553,6 +6562,14 @@ With a numeric prefix, show all headlines up to that level."
     (org-overview))
    ((eq org-startup-folded 'content)
     (org-content))
+   ((eq org-startup-folded 'show2levels)
+    (org-content 2))
+   ((eq org-startup-folded 'show3levels)
+    (org-content 3))
+   ((eq org-startup-folded 'show4levels)
+    (org-content 4))
+   ((eq org-startup-folded 'show5levels)
+    (org-content 5))
    ((or (eq org-startup-folded 'showeverything)
 	(eq org-startup-folded nil))
     (org-show-all)))