OFDM Synchronization example in matlab

I am reading the OFDM Synchronization example in Matlab and I have some questions in some codes.

In the OFDMReceiver.m file , function locatePreamble

How these length come?

windowLength = ceil(0.5*obj.FrameLength + length(obj.pPreamble));

rWin = x(1: windowLength-L+K-1);

PhatShort = Phat(ceil(length(Phat)/2):end-K/2+1);

if true
function preambleStartLocation = locatePreamble(obj, x)
  % Locate the starting point of the preamble using cross correlation.

    L = obj.FFTLength;
    K = obj.FFTLength/4; 
    known = obj.pPreamble(1:K);
    windowLength = ceil(0.5*obj.FrameLength + length(obj.pPreamble));

    % Cross correlate
    rWin = x(1: windowLength-L+K-1);
    Phat = xcorr(rWin, conj(known));
    Rhat = xcorr(abs(rWin).^2, ones(K,1)); % Moving average

    % Remove leading and tail zeros overlaps
    PhatShort = Phat(ceil(length(Phat)/2):end-K/2+1);
    RhatShort = Rhat(ceil(length(Rhat)/2):end-K/2+1);

    % Calculate timing metric
    M = abs(PhatShort).^2 ./ RhatShort.^2;

    % Determine start of short preamble. First find peak locations
    MLocations = find(M > (max(M)*obj.PeakThreshold));

    % Correct estimate to the start of preamble, not its center
    MLocations = MLocations - (K/2+1);

    % Determine correct peaks
    peaks = zeros(size(MLocations));
    desiredPeakLocations = (K:K:2*L)';
    for i = 1:length(MLocations)
        MLocationGuesses = MLocations(i) + desiredPeakLocations;
        peaks(i) = length(intersect(MLocations(i:end), MLocationGuesses));
    end

    % Have at least obj.pNumRequiredPeaks peaks for positive match    
    peaks(peaks < obj.MinNumPeaksForMatch) = 0;

    % Pick earliest peak in time
    [numPeaks, frontPeakLocation] = max(peaks);
    if ~isempty(peaks) && (numPeaks > 0)
        preambleStartLocation = MLocations(frontPeakLocation);
    else % No desirable location found
        preambleStartLocation = -1; 
    end
    % code
  end