Every setting is an expression.
A step's settings are values: a number written in, the event's block, a variable, or a function worked out from other values, such as the place three blocks above the player. The inspector offers what fits where the step stands, so a value is picked more often than typed.
Types.
Every value has a type: a number, text, yes or no, a player, a mob, a kind of block, a place, an area, or a list of any of those. A setting takes only what fits, and the editor says when something doesn't.
Text with placeholders.
Text carries colours and styles, such as <gold> and <bold>, and placeholders in braces: the player, the event's fields, variables, the clock. The preview shows it as the game will draw it.
Functions.
Functions take values and give one back: the nearest player, a random number, whether a player holds an item, the block at a place. They nest as deep as a value needs, and the reference lists every one with its signature.