Introduce the document structure.

org_mode_samples/sections_and_headings/Makefile

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+SHELL := bash
+.ONESHELL:
+.SHELLFLAGS := -eu -o pipefail -c
+.DELETE_ON_ERROR:
+MAKEFLAGS += --warn-undefined-variables
+MAKEFLAGS += --no-builtin-rules
+SRCFILES := $(wildcard *.org)
+OUTFILES := $(patsubst %.org,%.tree.txt,$(SRCFILES))
+
+ifeq ($(origin .RECIPEPREFIX), undefined)
+  $(error This Make does not support .RECIPEPREFIX. Please use GNU Make 4.0 or later)
+endif
+.RECIPEPREFIX = >
+
+.PHONY: all
+all: $(OUTFILES)
+
+.PHONY: clean
+clean:
+> rm -rf $(OUTFILES)
+
+%.tree.txt: %.org ../common.el ../dump_org_ast.bash
+> ../dump_org_ast.bash $< $@

org_mode_samples/sections_and_headings/immediate_heading.org

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+* Start a document with an immediate heading

org_mode_samples/sections_and_headings/sections_and_headings.org

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+Before the first heading
+* The first heading
+body of the first section
+** Child heading
+body of child heading
+* second top-level heading
+body of second top-level heading