﻿Some syntax I use on this document
: type
?= possible values
" types it works it
~" ingame or "outgame"
~% only works on screen 
?% only works on
!% doesn't work on
! not
&& and
| or
... can have a custom value

More info here: Bedrock JSON UI - Explained.docx
You can find the #item_aux_id values here https://lukaspah.github.io/item_aux_calculator/item_id_aux.html. Made by @LukasPAH.

namespace: string ?= ...
Properties
type: string ?= panel - stack_panel -  label - image - input_panel - custom - grid - factory - button - toggle - slider - dropdown -  edit_box - scoll_view  - screen - selection_wheel " any
size: (number|string)[] = [0, 0] ? 0 - "0px" - "0%" - "0%x" - "0%y" - "0%cm" - "0%sm" - "default" - "fill" " any
max_size: (number|string)[] = [0, 0] ? 0 - "0px" - "0%" - "0%x" - "0%y" - "0%cm" - "0%sm" - "default" - "fill" " any!?custom
min_size: (number|string)[] = [0, 0] ? 0 - "0px" - "0%" - "0%x" - "0%y" - "0%cm" - "0%sm" - "default" - "fill" " any!?custom
collection_name: string " stack_panel/grid/factory
controls: array({}) " any
anchor_from: string ?= top_left - top_middle - top_right - left_middle - center - right_middle - bottom_left - bottom_middle - bottom_right " any
anchor_to: string ?= top_left - top_middle - top_right - left_middle - center - right_middle - bottom_left - bottom_middle - bottom_right " any
orientation: string ?= vertical - horizontal " stack_panel
color: string|number[](float|int, >= 0) ?= [0, 0, 0] - white - black - red - yellow - blue " label/image
locked_color string|number[](float|int, >= 0) ?= [0, 0, 0] - white - black - red - yellow - blue " label/image
text: string " label
font_type: string ?= default - smooth - rune - MinecraftSeven - MinecraftTen - MinecraftTenEmoticon " label
collection_index: number(int) " any!custom
layer: number(int) " any
bilinear: boolean " image/custom(panorama_renderer)
font_scale_factor: number(float, > 0) " label
font_size: string ?= normal - small - large - extra-large " label
text_alignment: string ?= left - center - right " label
keep_ratio: boolean " image
fill: boolean " image
zip_folder: string " image
texture_file_system: string " image
$fit_to_width: boolean " image
force_texture_reload: boolean " image
grayscale: boolean " image
uv: number(int, >= 0)[] ? [0, 0]/... " image
uv_size: number(int, >= 0)[] ? [0, 0]/... " image
offset: (number|string)[] ? [0, 0] ? 0 - 0px - 0% - 0%x - 0%y - 0%cm - 0%sm " any
focus_change_up: string ?= FOCUS_OVERRIDE_STOP/... " button/toggle/slider/input_panel
focus_change_down: string ?= FOCUS_OVERRIDE_STOP/... " button/toggle/slider/input_panel
focus_change_left: string ?= FOCUS_OVERRIDE_STOP/... " button/toggle/slider/input_panel
focus_change_right: string ?= FOCUS_OVERRIDE_STOP/... " button/toggle/slider/input_panel
focus_identifier: string " button/toggle/slider/input_panel
focus_enabled: boolean " button/toggle/slider/input_panel
focus_wrap_enabled: boolean " button/toggle/slider
focus_magnet_enabled: boolean " button/toggle/slider
focus_container: boolean " panel/input_panel/stack_panel
use_last_focus: boolean " panel/input_panel/stack_panel
focus_nagivation_mode_up: string ?= {EMPTY} - none - stop - custom - contained " panel/input_panel/stack_panel
focus_nagivation_mode_down: string ?= {EMPTY} - none - stop - custom - contained " panel/input_panel/stack_panel
focus_nagivation_mode_left: string ?= {EMPTY} - none - stop - custom - contained " panel/input_panel/stack_panel
focus_nagivation_mode_right: string ?= {EMPTY} - none - stop - custom - contained " panel/input_panel/stack_panel
focus_container_custom_up: array({}) " panel/input_panel/stack_panel
      other_focus_container_name: string
focus_container_custom_down: array({}) " panel/input_panel/stack_panel
focus_container_custom_left: array({}) " panel/input_panel/stack_panel
focus_container_custom_right: array({}) " panel/input_panel/stack_panel
always_listen_to_input: boolean " input_panel/slider/scroll_view/?...
always_handles_pointer: boolean " slider/scroll_view/button/?...
follows_cursor: boolean " button/image/?...
shadow: boolean " text
localize: boolean " text
enable_profanity_filter: boolean " text
notify_on_ellipses: string[] " text
hide_hyphen: boolean " text
tts_inherit_siblings: boolean " stack_panel/panel/input_panel/label/image
color1: color + alpha ? [0, 0, 0, 0] " custom(gradient_renderer)
color2: color + alpha ? [0, 0, 0, 0] " custom(gradient_renderer)
constrain_to_rect: boolean " edit_box
selected: boolean " edit_box
can_be_deselected: boolean " edit_box
camera_tilt_degrees: number(int, >= - 90 && <= 90)? " custom(paper_doll_renderer)
starting_rotation: number(int, >= - 90 && <= 90)? " custom(paper_doll_renderer)
use_uuid: boolean " custom(paper_doll_renderer)
use_selected_skin: boolean " custom(paper_doll_renderer)
use_skin_gui_scale: boolean " custom(paper_doll_renderer)
use_player_paperdoll: boolean " custom(paper_doll_renderer)
use_scissor_test: boolean " custom(actor_portrait_renderer/paper_doll_renderer)
rotation: string ?= gesture_x - ?... " custom(paper_doll_renderer/panorama_renderer)
primary_color: color + alpha ? [0, 0, 0, 0] " custom(progress_bar_renderer)
use_priority: boolean " any?
priority: number(int, >= 0) " any
tiled: boolean " image
tiled: string ?= y - x " image
tiled_scale: number(float)[] ?= [0, 0]/... " image
inherit_max_sibling_height: boolean " panel/stack_panel/image/label/grid
inherit_max_sibling_width: boolean " panel/stack_panel/image/label/grid
always_listening: boolean " text_box
max_length: number(int, >= 1) " text_box
clips_children: boolean " any!custom
clip_direction: string ?= left  - right - up - down " image
clip_pixelperfect: boolean " image
anims: string[] " any
animation_reset_name: string ?= screen_animation_reset " any
allow_clipping: boolean " any!?custom
ignored: boolean " any
visible: boolean " any
enabled: boolean " any
modal: boolean " input_panel
renderer: boolean " custom
inline_modal: boolean " input_panel
hover_enabled: boolean " input_panel
prevent_touch_input: boolean " input_panel
gesture_tracking_button: string " input_panel
always_handle_controller_direction: boolean " input_panel
ttsSectionContainer: boolean " input_panel/grid/panel/stack_panel
alpha: number(float, >= 0 && <= 1) " any!?custom
locked_alpha: number(float, >= 0 && <= 1) " any!?custom
propagate_alpha: boolean " any!?custom
disable_anim_fast_forward: boolean " any
clip_state_change_event: string " stack_panel/panel/grid/?...
tts_override_control_value: number(float) " button/toggle/slider/...
grid_item_template: string " grid
maximum_grid_items: number(int, >= 1) " grid
grid_dimensions: number(int, >= 0)[] ?= [0, 0]/... " grid
grid_dimension_binding: string " grid
grid_fill_direction: string ?= vertical - horizontal " grid
grid_rescaling_type: string ?= vertical - horizontal " grid
grid_position: number(int, >= 0)[] ?= [0, 0]/... " any!grid/custom
anim_type: string ?= flip_book - offset - alpha - size - wait
initial_uv: number(int)[] = [0, 0] " flip_book
frame_count: number(int, >= 1) " flip_book
frame_steps: number(int, >= 1) " flip_book
reversible: boolean " flip_book
scale_from_starting_alpha: boolean " anim_type: alpha
fps: number(int, >= 1) " flip_book
easing: number(int, >= 1) ?= linear - spring - in_sine - in_quart - in_quint - in_expo - out_expo - out_cubic - out_back " any(anim_type)
duration: number(float, >= 0) " any(anim_type)
from: number(alpha)|number[](size|offset) ) " any(anim_type)!wait
to: number(alpha)|number[](size|offset) ) " any(anim_type)!wait
destroy_at_end: string " any(anim_type)
next: string ?= @NAMESPACE.NAME " any(anim_type)
resettable: boolean " any(anim_type)!?flip_book
play_event: string " any(anim_type)!flip_book/?...
end_event: string " any(anim_type)!flip_book/custom(credits_renderer)/?...
text_color:
background_color
button_mappings: array({}) " button/toggle/slider/input_panel/scroll_view
      from_button_id: string ?= {Button Ids(From)}
      to_button_id: string ?= {Button Ids(To), Button Names}
handle_select: boolean
handle_deselect: boolean
      mapping_type: string ?= pressed - focused - global
      scope: string ?= view - controller
      input_mode_condition: string ?= gamepad_and_not_gaze - not_gaze
      button_up_right_of_first_refusal: boolean
variables: array({})|Object " any
requires: string
factory: Object " stack_panel
      name: string ?= {Factory Names}
      control_ids: object
      factory_variables: array({})
bindings: array({}) " any
      binding_name: string ?= {Binding Names}
      binding_name_override: string ?= {Binding Names, !...}
      binding_collection_name: string ?= {Collection Names}
      binding_collection_prefix: string
      binding_type: string ?= global - view - collection - collection_details
      binding_condition: string ?= once - visible - always - always_when_visible
      source_control_name: string
      source_property_name: string
      target_property_name: string
      resolve_sibling_scope: boolean
property_bag: Object " any
modifications: array({}) " any
sound_name: string " button/toggle
sound_volume: number(float, >= 0 ?&& <= 1) " button/toggle
sound_pitch: number(float, >= 0 ?&& <= 1) " button/toggle
default_control: string ?= default/... " button
hover_control: string ?= hover/... " button
pressed_control: string ?= pressed/... " button
indent_control: string ?= indent/... " type: slider_box
locked_control: string ?= locked/... " button
unchecked_control: string ?= unchecked/... " toggle
unchecked_hover_control: string ?= unchecked_hover/... " toggle
unchecked_locked_control: string ?= unhecked_locked/... " toggle
unchecked_locked_hover_control: string ?= unchecked_locked_hover/unchecked_locked/... " toggle
checked_control: string ?= checked/... " toggle
checked_hover_control: string ?= checked_hover/... " toggle
checked_locked_control: string ?= checked_locked/... " toggle
checked_locked_hover_control: string ?= checked_locked_hover/checked_locked/... " toggle
slider_box_control: string ?= default/... " slider
default_focus_precedence: number(int, >= 0) " button/toggle/slider
reset_on_focus_lost: string ?= unchecked/... " toggle/?...
toggle_name: string ?= ... " toggle
radio_toggle_group: boolean " toggle
toggle_group_forced_index: number(int) " toggle
toggle_group_default_selected: number(int) " toggle
toggle_grid_collection_name: string " toggle
toggle_default_state: boolean " toggle
slider_name: string " slider
slider_track_button: string " slider
slider_direction: string ?= vertical - horizontal " slider
slider_steps: number(int, >= 1) " slider
slider_collection_name: string " slider
slider_small_discrease_button: string " slider
slider_small_increase_button: string " slider
slider_selected_button: string " slider
slider_deselected_button: string " slider
slider_select_on_hover: boolean " slider

tts_name: string " toggle/button/slider
tts_control_header: string " toggle/button/slider
tts_section_header: string " toggle/button/slider
tts_control_type_order_priority: number(int) " toggle/button/slider
tts_index_priority: number(int) " toggle/button/slider
tts_toggle_on: string " toggle
tts_toggle_off: string " toggle
tts_value_changed: string " slider

send_telemetry: boolean " screen
screen_not_flushable: boolean " screen
is_modal: boolean " screen
is_showing_menu: boolean " screen
render_game_behind: boolean " screen
low_frequency_rendering: boolean " screen
send_telemetry: boolean " screen
should_steal_mouse: boolean " screen
render_only_when_topmost: boolean " screen
screen_draws_last: boolean " screen
force_render_below: boolean " screen
always_accepts_input: boolean " screen
close_on_player_hurt: boolean " screen ~" ingame
Custom Renderers
flying_item_renderer ~" ingame
inventory_item_renderer ~" ingame (the items/blocks item icon)
credits_renderer ~% credits_screen
vignette_renderer
name_tag_renderer
paper_doll_renderer
debug_screen_renderer ~% debug_screen
enchanting_book_renderer ~% enchanting_table_screen ~" ingame
gradient_renderer
live_horse_renderer ~% horse_screen ~" ingame
live_player_renderer ~" ingame
hud_player_renderer ~" ingame
hotbar_renderer ~" ingame
hotbar_cooldown_renderer ~" ingame
heart_renderer ~" ingame
horse_heart_renderer ~" ingame
armor_renderer ~" ingame
horse_jump_renderer ~" ingame
hunger_renderer ~" ingame
bubbles_renderer ~" ingame
mob_effects_renderer ~" ingame
cursor_renderer ~" ingame (crosshair)
progress_indicator
camera_renderer ~" ingame
web_view_renderer
banner_pattern_renderer ~" ingame
actor_portrait_renderer
trial_time_renderer
progress_bar_renderer
3d_structure_renderer ~% structure_editor_screen ~" ingame
splash_text_renderer
hover_text_renderer
ui_holo_cursor
panorama_renderer ~% store (It's not the panoramas that appear behind the menus. It's the panorama of the worlds on the store.)
Hardcoded Variables
$trial (if it is in the trial version of the game)
$is_publish (if it is public and not a developer version)
$is_pregame (if it is "outgame" not ingame)
$is_xbox_live_enabled 
$desktop_screen (if the classic UI is selected)
$pocket_screen (if the pocket UI is selected)
$win10_edition
$pocket_edition
$education_edition
$education_edition_china
$console_edition
$osx_edition
$nx_edition
$fire_tv
$gear_vr
$supports_cross_platform_play_toggle
$ignore_profile_switch_account_button
$ignore_profile_sso_toggle
$is_settopbox
$is_reality_mode
$storage_location_switch_enabled
$thirdpartyconsole
$is_ps4
$psvr
$supports_hand_controllers
$is_ios/$ios
$is_android
$is_win10_arm
$display_copyright_info
$is_windows_10_mobile
$device_must_be_removed_for_xbl_signin
$build_platform_UWP
$requires_xbl_signin_to_play
$supports_user_configured_safezone
$can_splitscreen
Property Bag/Binding Names
#visible: boolean " any
#enabled: boolean !% source_property_name " any
#text " text
#hyperlink: string = HARDCODED VALUES ONLY " button
#tts_dialog_title: string " text
#tts_dialog_body: string" text
#property_field: string " edit_box
#flying_item_renderer: boolean " custom(flying_item_renderer) ~" ingame
#item_id_aux: number(int) " custom(inventory_item_renderer) ~" ingame
#collection_name: string
#collection_index: number(int, >= 0)
opacity_override: number(float, >= 0) " custom(vignette)
#playername: string " custom(name_tag_renderer)
#x_padding: number(int, >= 0) " custom(name_tag_renderer)
#skin_rotation: boolean " custom(paper_doll_renderer)
#index: number(int, >= 0) " any!?
#hover_slice: number(int, >= 0) " selection_wheel
#filtered_light_multiplier: number(float, >= 0) " custom(inventory_item_renderer)
#start_selected
#sub_command
#button_navigation
#panel_title: string " toggle
force_update: boolean " custom(inventory_item_renderer)/?...
#use_heart_offset: boolean " custom(armor_renderer) ~" ingame
#look_at_cursor: boolean " custom(live_player_renderer)
#visible_after_x_ratings
#default_prompt_color: color " image(!important it only works with the offer prompt on the store)
#coin_prompt_color: color " image(!important it only works with the offer prompt on the store)
control_id
#max_upsell_offers
#common: color " image(!important it only works on the item rarity for the character creator)
#uncommon: color " image(!important it only works on the item rarity for the character creator)
#rare: color " image(!important it only works on the item rarity for the character creator)
#epic: color " image(!important it only works on the item rarity for the character creator)
#legendary: color " image(!important it only works on the item rarity for the character creator)
#is_featured
#preview_idx: number(int, >= 0) " custom(paper_doll_renderer)/?...
#anchored_offset_value_x: number(int) " image
#anchored_offset_value_y: number(int) " image
#timer_field_count_to_show
#timer_duration
#collection_prefix: number(int, >= 0)
#has_focus: boolean
#block_position: number[] ? [0, 0, 0] " custom(3d_structure_renderer) ~" ingame
#bottom_left_block: number[] ? [0, 0, 0] " custom(3d_structure_renderer) ~" ingame
#top_left_block: number[] ? [0, 0, 0] " custom(3d_structure_renderer) ~" ingame
#include_entities: boolean " custom(3d_structure_renderer) ~" ingame
#remove_blocks: boolean " custom(3d_structure_renderer) ~" ingame
#include_players: boolean " custom(3d_structure_renderer) ~" ingame
#toggle_state: boolean " toggle
#slider_value: number(int, >= 0) " slider
#is_dropdown: boolean " input_panel
is_durability: boolean " custom(progress_bar_renderer) ~" ingame
round_value: boolean " custom(progress_bar_renderer)
#flying_item_renderer " custom(flying_item_renderer) ~" ingame
reset_group " button((action))
#should_host: boolean

Collection Names
popular_packs_collection
content_sections
platform_terms_collection
keyboard_full_collection ~% settings_screens
keyboard_standart_collection ~% settings_screens
gamepad_collection ~% settings_screens
Factory Names
platform_terms_factory
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
Button Names
button.select_offer
button.action_button
button.create_realm
button.tos_hyperlink
button.privpol_hyperlink
button.tos_popup
button.privpol_popup
button.binding_button
button.reset_binding ~% settings_screens
button.reset_keyboard_bindings ~% settings_screens
button.view_account_errors
button.switch_accounts
button.open_content_log_history
button.clear_content_log_files
button.clear_msa_token_button
button.terms_and_conditions_popup
button.credits ~% settings_screens
button.unlink_msa
button.attribute_popup
button.licensed_content
button.font_license
Button Ids
From:
button.menu_cancel
button.controller_secondary_select

To:
button.menu_exit
button.search
      
Binding Names
#visible ?% target_property_name/source_property_name/binding_name_override " any
#toggle_state ?% binding_name_override/source_property_name " any

#key_art_texture_file_system " image
#texture_file_system " image
#key_art_texture_path " image
#texture " image

#content_tab_sections ~% realms plus
#collection_length ~% any " any
#packs_label ~% realms plus
#right_most_grid_item_focus_override_right
#focus_change_right
#buy_visible

#realms_plus_one_month_free_trial_visible
#realms_plus_one_month_free_trial_not_visible
#has_checked_tos

#landing_info_line_4
#landing_info_line_5
#content_section_text
#faq_price_text
#platform_terms_text
#trial_desciption_text
#buy_now_banner_text
#binding_button_text
#content_log_location_text

#ad_account_name

#buy_now_button_text
#page_loading_visible
#binding_icon_sprite
#keymapping_name
#audible_keymapping_name
#keyboard_show_standart_keyboard_options ~% settings_screens
#keyboard_show_full_keyboard_options ~% settings_screens
#vr_roll_turn_sensitivity_visible
#content_log_gui_option_enabled
#allow_content_log_write_to_disk
#content_log_file_enabled
#has_account_error
#can_change_name
#not_logged_in
#logged_in
#hyperlink
#terms_and_conditions_hyperlink
