The ST backend edits IEC 61131-3 Structured Text: POUs, variable sections, methods, structs and enums, with the file parsed so the colouring, the outline and the completion lists all come from what the file declares.

a .st file open, Variables above Body, with the splitter between them

One POU, two panes

A POU is edited as two panes with a splitter between them:

Variables — VAR, VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, VAR_EXTERNAL, VAR_GLOBAL, VAR_TEMP
Body — the cyclic code

Where the splitter sits is remembered per workspace in undoApp.Editor.ini.

Methods

A FUNCTION_BLOCK has method tabs beside the POU tab; PROGRAM and FUNCTION do not, because they have no methods in ST. Tabs can be dragged to reorder them.

**+** adds a method, asking for its name and return type rather than inventing one
Right-click a method tab for Delete Method, with a confirmation
Add Method in a file's context menu in the Workspace tree does the same thing

Saving or compiling serializes every tab of the POU, not only the one on screen. The editors for a method are created the first time the tab is opened and kept after it.

The toolbar

Button
Save	writes the whole POU, every method tab included
Compile	hands the project to st2cpp — see output.md
Validate	parses and analyses without generating
Close	closes the document
Tooltips	off by default; see autocomplete.md

Semantic colouring

Identifiers are coloured by what they resolve to — a declared variable, a function, a type, a keyword — using the symbol table st2cpp builds, not a keyword list. A name that resolves to nothing is left uncoloured, which is how a typo shows up before it is compiled.

The outline

The ST Outline panel shows the parsed structure: each POU, its variable sections and the declarations in them, its methods, and the file's structs and enums. It is empty until a valid file is open, and it says so.

Keyboard

Key
`Ctrl+S`	save
`Ctrl+N`	new POU
`Ctrl+W`	close the document
`Ctrl+Click`	go to the declaration of the identifier under the cursor

The rest are in keyboard.md.