Placeholders are supported in the following properties in menus: Placeholders are supported in the following properties in icons:

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Built-In Placeholders

These placeholders are included in ElvenideGUI and do not require a placeholder plugin. Built-in placeholders are surrounded in curly braces ({placeholder}) for backwards compatibility with Chest Commands placeholders.
PlaceholderDescription
{player}The username of the player viewing the menu.
{money}The amount of money the player has. Requires an installed economy.
{world}The name of the world the player is in.
{online}The number of players currently on the server.
{max_players}The maximum number of player slots in the server.
{uuid}The UUID of the player viewing the menu.
{display_name}The display name or nickname of the player viewing the menu.
{ping}The connection ping of the player, in milliseconds.

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PAPI Placeholders

If you have the PlaceholderAPI plugin installed, you can use its placeholders and placeholders that other plugins have registered with it. PlaceholderAPI (or PAPI) placeholders are surrounded in percent signs (%placeholder%). You can find a very long list of some PAPI placeholders here.

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Your Own Placeholders

You can create your own custom placeholders with static text, usable across all menus. They can be added in the /plugins/ElvenideGUI/config/placeholders.conf file. Although the file ends in .conf, it is treated as a YML file.
Unlike the built-in and PAPI placeholders, there is no surrounding symbol requirement; you could use curly braces, percent signs, brackets, or even no symbols at all
Some Custom Placeholders
# Generated by default on first plugin load
'{star}': '★'
'{heart}': '❤'
'{u_arr}': '⬆'
'{d_arr}': '⬇'
'{l_arr}': '⬅'
'{r_arr}': '➡'

# Some extra ones
'((my_name))': 'Elvenide'
'[server_name]': 'Zombiehorde.net'
Using the custom placeholders in the above example, the following menu title: 
title: '{star} StarCraft {star}'
Would display in-game as the following: 
★ StarCraft ★