I remove [1:] elements from every array and got this file, it shows how sublime text save session data. Main content are in window[n]-buffers, selection and buffer settings are in window[n]-groups[n]-sheets[n].

sublime_text_session_file_structure_example.json

{
    "workspaces": {
        "recent_workspaces": [
        	"/D/coding/project/demo.sublime-workspace"
        ]
    },
    "settings": {
        "new_window_settings": {
            "menu_visible": true,
            "output.mdpopups": {
                "height": 0.0
            },
            "status_bar_visible": true,
            "output.jotter": {
                "height": 139.0
            },
            "output.exec": {
                "height": 278.0
            },
            "output.composer": {
                "height": 151.0
            },
            "replace": {
                "height": 77.0
            },
            "output.find_results": {
                "height": 0.0
            },
            "build_system_choices": [
                [
                    [
                        [
                            "Anaconda Python Builder",
                            ""
                        ]
                    ]
                ]
            ],
            "file_history": [
            	"/D/PortableSoftware/SublimeText3/Data/Packages/PHP Completions Kit/README.md",
            ],
            "find": {
                "height": 44.0
            },
            "command_palette": {
                "width": 844.0,
                "selected_items": [
                    [
                        "php syn",
                        "Set Syntax: PHP"
                    ]
                ],
                "last_filter": "",
                "height": 392.0
            },
            "console": {
                "height": 270.0,
                "history": [
                	"print(\"\\n\"*20)"
                ]
            },
            "select_symbol": {
                "width": 448.0,
                "selected_items": [],
                "last_filter": "",
                "height": 400.0
            },
            "output.SublimeLinter Messages": {
                "height": 309.0
            },
            "select_file": {
                "width": 0.0,
                "selected_items": [
                    [
                        "",
                        "C:\\info.php"
                    ]
                ],
                "last_filter": "",
                "height": 0.0
            },
            "find_state": {
                "regex": true,
                "whole_word": false,
                "show_context": true,
                "in_selection": false,
                "preserve_case": false,
                "use_buffer2": true,
                "replace_history": [
                	"\\t",
                ],
                "case_sensitive": true,
                "find_history": [
                	"%\\d\\$",
                ],
                "wrap": true,
                "highlight": true,
                "reverse": false
            },
            "select_project": {
                "width": 380.0,
                "selected_items": [
                    [
                        "",
                        "C:\\SublimeText3\\demo.sublime-workspace"
                    ]
                ],
                "last_filter": "",
                "height": 500.0
            },
            "auto_complete": {
                "selected_items": [
                    [
                        "exp",
                        "explode〔function〕"
                    ]
                ]
            },
            "input": {
                "height": 50.0
            },
            "incremental_find": {
                "height": 30.0
            },
            "find_in_files": {
                "where_history": [
                	"<open files>",
                ],
                "height": 126.0
            },
            "show_open_files": true,
            "output.package_dev": {
                "height": 145.0
            },
            "save_all_on_build": true,
            "side_bar_visible": true,
            "distraction_free": {
                "menu_visible": true,
                "status_bar_visible": false,
                "show_open_files": false,
                "show_tabs": false,
                "side_bar_visible": false,
                "show_minimap": false
            },
            "pinned_build_system": "",
            "output.reg_replace": {
                "height": 580.0
            },
            "output.SublimeLinter": {
                "height": 312.0
            },
            "template_settings": {},
            "output.tooltips": {
                "height": 151.0
            },
            "build_varint": "",
            "side_bar_width": 216.0,
            "show_tabs": false,
            "show_minimap": true
        },
        "new_window_width": 143.2,
        "new_window_height": 479.2
    },
    "windows": [
        {
            "menu_visible": true,
            "output.mdpopups": {
                "height": 0.0
            },
            "selected_group": 0,
            "output.jotter": {
                "height": 139.0
            },
            "output.exec": {
                "height": 278.0
            },
            "output.composer": {
                "height": 151.0
            },
            "replace": {
                "height": 77.0
            },
            "output.find_results": {
                "height": 0.0
            },
            "build_system_choices": [
                [
                    [
                        [
                            "Anaconda Python Builder",
                            ""
                        ]
                    ]
                ]
            ],
            "file_history": [
            	"/D/info.php",
            ],
            "find": {
                "height": 44.0
            },
            "buffers": [
            	[
            	],
                {
                    "contents": "some demo text here\n\n",
                    "settings": {
                        "buffer_size": 21,
                        "name": "some demo text here",
                        "line_ending": "Unix"
                    }
                }
            ],
            "command_palette": {
                "width": 844.0,
                "selected_items": [
                    [
                        "install",
                        "Package Control: Install Package"
                    ]
                ],
                "last_filter": "",
                "height": 392.0
            },
            "expanded_folders": [
                "/D/coding/projects",
                "/D/coding/projects/demo"
            ],
            "console": {
                "height": 270.0,
                "history": [
                	"print(\"\\n\"*20)"
                ]
            },
            "select_symbol": {
                "width": 448.0,
                "selected_items": [],
                "last_filter": "",
                "height": 400.0
            },
            "output.SublimeLinter Messages": {
                "height": 309.0
            },
            "select_file": {
                "width": 0.0,
                "selected_items": [
                    [
                        "",
                        "C:\\info.php"
                    ]
                ],
                "last_filter": "",
                "height": 0.0
            },
            "find_state": {
                "regex": true,
                "whole_word": false,
                "show_context": true,
                "in_selection": false,
                "preserve_case": false,
                "use_buffer2": true,
                "replace_history": [
                	"\\t",
                ],
                "case_sensitive": true,
                "find_history": [
                	"%\\d\\$",
                ],
                "wrap": true,
                "highlight": true,
                "reverse": false
            },
            "select_project": {
                "width": 380.0,
                "selected_items": [
                    [
                        "",
                        "C:\\SublimeText3\\demo.sublime-workspace"
                    ]
                ],
                "last_filter": "",
                "height": 500.0
            },
            "status_bar_visible": true,
            "auto_complete": {
                "selected_items": [
                    [
                        "array",
                        "array_chunk"
                    ]
                ]
            },
            "input": {
                "height": 50.0
            },
            "incremental_find": {
                "height": 30.0
            },
            "build_system": "Packages/Python/Python.sublime-build",
            "output.package_dev": {
                "height": 145.0
            },
            "find_in_files": {
                "where_history": [
                	"<open files>",
                ],
                "height": 126.0
            },
            "window_id": 249,
            "show_open_files": true,
            "groups": [
                {
                    "selected": 154,
                    "sheets": [
                        {
                            "buffer": 0,
                            "stack_index": 4,
                            "semi_transient": false,
                            "type": "text",
                            "settings": {
                                "translation.x": 0.0,
                                "translation.y": 0.0,
                                "settings": {
                                    "default_dir": "C:\\demodir",
                                    "bracket_highlighter.clone_regions": [
                                    	"bh_curly",
                                    ],
                                    "encoding_helper_encoding": "",
                                    "bracket_highlighter.clone_locations": {
                                        "close": {},
                                        "open": {},
                                        "unmatched": {},
                                        "icon": {}
                                    },
                                    "bracket_highlighter.busy": false,
                                    "bracket_highlighter.regions": [
                                    	"bh_round",
                                    ],
                                    "is_init_dirty_state": true,
                                    "auto_name": "some demo text here",
                                    "is_xml": false,
                                    "word_wrap": false,
                                    "bracket_highlighter.locations": {
                                        "close": {},
                                        "open": {},
                                        "unmatched": {},
                                        "icon": {}
                                    },
                                    "SL.13.region_keys": [],
                                    "syntax": "Packages/Text/Plain text.tmLanguage",
                                    "bracket_highlighter.clone": -1
                                },
                                "zoom_level": 1.0,
                                "regions": {},
                                "selection": [
                                    [
                                        728,
                                        728
                                    ]
                                ],
                                "buffer_size": 1593
                            }
                        }
                    ]
                }
            ],
            "workspace_name": "/D/coding/projects/demo.sublime-workspace",
            "save_all_on_build": true,
            "side_bar_visible": true,
            "distraction_free": {
                "menu_visible": true,
                "status_bar_visible": false,
                "show_open_files": false,
                "show_tabs": false,
                "side_bar_visible": false,
                "show_minimap": false
            },
            "pinned_build_system": "",
            "layout": {
                "cells": [
                    0
                ],
                "rows": [
                    0.0,
                    1.0
                ],
                "cols": [
                    0.0,
                    1.0
                ]
            },
            "output.reg_replace": {
                "height": 580.0
            },
            "output.SublimeLinter": {
                "height": 312.0
            },
            "settings": {},
            "output.tooltips": {
                "height": 151.0
            },
            "template_settings": {},
            "project": "demo.sublime-project",
            "build_varint": "",
            "side_bar_width": 216.0,
            "position": "0,2,3,-1,-1,-1,-1,563,26,26,184",
            "show_tabs": false,
            "show_minimap": true
        }
    ],
    "last_version": 3211,
    "log_indexing": false,
    "folder_history": [
    	"/D/coding/projects/demo",
    ],
    "last_window_id": 258
}