[a]

Valid

Starts with a letter.

[A]

Valid

Field is equivalent to [a] because field names are case insensitive.

[OdD CaSE]

Valid

Field names are case insensitive.

[Company Name]

Valid

Contains only letters and spaces.

[This is a long field]

Valid

It has less than 50 characters.

[I should totally start thinking about making my field names shorter]

Not valid

Field names are limited to 50 characters.

[Field number 1]

Valid

Numbers are allowed after the first character.

[1]

Not valid

Field names cannot start with a number; they must start with a letter.

[Mary had 1 little lamb]

Valid

Numbers are allowed after the first character.

[A "peculiar" field]

Not Valid

Fields can only contain letters and digits.

[A field with punctuation.]

Not Valid

Fields can only contain letters and digits.

CompanyName

Not valid

Not enclosed in brackets.

[ ]

Not valid

Field names must start with a letter.